If you’re considering a heat pump or had one recently installed, this article is for you. Our six-year journey with a heat pump has been a rollercoaster of expensive mistakes, lessons learned and a mission to help others avoid our pitfalls. Heat pumps are incredible technology when installed and designed correctly. But when things go wrong, they can become a source of great frustration. Here’s what you need to know to ensure your heat pump journey is a success.
The Start of Our Heat Pump Journey
Six years ago, after an extensive vetting process, we appointed Global Energy Systems to install our air source heat pump. Global Energy Systems supplied the unit and subcontracted the physical installation to another MCS-accredited company, All Seasons Energy, while maintaining the full contract with us.
From the very beginning, it was evident something was amiss. The first three winters were plagued with issues: rooms that wouldn’t heat properly, issues with the controls and higher than expected running costs, temporarily obscured by the cushion of cheap electricity tariffs at the time.
Each time Global Energy Systems dispatched a team to address our concerns, we talked ourselves into believing things had improved – perhaps out of desperation to justify the £16,000 investment in the system. But as soon as the next cold spell hit, the same problems reared their ugly heads. In hindsight, it’s glaringly obvious: the installation wasn’t just flawed – it was fundamentally botched from the start.
A System That Was Never Designed to Work
One of the biggest revelations came years later as we gradually started to educate ourselves on low temperature heating: our system as a whole was never designed to work properly with a heat pump. Instead, it was slapped in to run like a boiler. This critical error was evident from the start, but we didn’t know enough then to question it.
The heating services and operations engineer from Global Energy Systems commissioned our system to run on a 45°C set point – a decision that is utterly indefensible if you understand how heat pumps should work. Heat pumps are designed to operate most efficiently at lower flow temperatures: the higher the flow temperature, the more energy they consume, driving up costs and eroding efficiency. Shockingly, when we inquired about weather compensation – a feature that optimises system performance by adjusting flow temperatures based on outdoor conditions – Global Energy Systems outright denied that their heat pump had this capability.
This was a blatant lie. Years later, after tinkering with the control panel, we discovered weather compensation settings and heat curve adjustments buried in the system. Global Energy Systems, it seems, had deliberately chosen to run the system at a fixed 45°C, not for our benefit, but to mask deeper issues with the system’s design and performance.
As we learned more about heat pumps, we suspected that a proper heat loss calculation and heating design had never been done. When we confronted Global Energy Systems, they admitted it hadn’t. This was a massive blunder. Proper heat loss calculations are the cornerstone of any heat pump installation. Without them, you’re essentially flying blind, which explains the inadequacies of our system.
The Saga of Cold Rooms and Circulation Pumps
For years, cold spells exposed more limitations of our system. The north end of our house – where the index circuit is – struggled to exceeded 16°C when outdoor temperatures dropped below 3°C. Global Energy Systems’ solution? Add more or upsize circulation pumps. We now have four, and they haven’t resolved the problem. Instead, they’ve increased our running costs.
When we had our system evaluated by some of the UK’s top installers, their feedback was unanimous: the system had no design and was set up to fail. As Ken Bone explains in the video below, it was essentially running as a boiler replacement with a Delta-T of 20, littered with on/off stats, which is unsuitable for a heat pump. Our house as a whole never had a chance of being heated efficiently.
Lessons Learned
Insist on a Proper System Design
Before installation, double, triple and quadruple-check that your system is designed properly. Ensure every room and heat emitter can hit its target temperature (19°C, 20°C or 21°C, depending on your preference). Get this in writing. These temperatures must be achievable when running weather compensation. Don’t let your installer convince you to settle for a fixed flow temperature. In mild months, this approach wastes energy and money.
Understand the Importance of Controllers
Heat pumps are fundamentally all very similar at their core: a metal box with pipes, refrigerant and a compressor. The controller, however, is what determines how effectively the system runs and does what you want it to do. In our case, the controller from Global Energy Systems has been dreadful. As we have a hybrid system, it can’t even run weather compensation if we wanted to use the boiler as a redundancy. Below 0°C, we’d have to manually turn the boiler on, which defeats the purpose of automation. There’s no scheduling. Frankly, there’s a lot missing. Opt for a brand that has a good controller.
Know Your Warranty Terms
Many warranties are tied to annual servicing. In our case, as per the warranty document, only Global Energy Systems could service the unit for the warranty to remain valid. This wasn’t communicated clearly upfront, leaving us at the mercy of the manufacturer. In addition to this, our unit came with a paltry three year warranty. Always ask about warranty terms and ensure you’re comfortable with them before committing. If something goes wrong, replacement components can be costly, so you have to ensure you’re covered for the longest time possible.
Look for Free Remote Monitoring Options From the Manufacturer
Global Energy Systems provided a three-year remote monitoring service via 4g, which allowed them to diagnose issues remotely. After that, they charge an annual fee. In contrast, some manufacturers like Mitsubishi offer free remote connectivity and telephone support for diagnosing problems. Check if your chosen manufacturer includes this service without additional charges. I’d also recommend that this connection is done via WiFi.
Don’t Settle for Less
If something feels off, don’t make excuses. We convinced ourselves that our system was working fine when it clearly wasn’t. Heat pumps, when installed correctly, keep you warm and comfortable. Don’t settle for anything less.
A Cautionary Tale with a Purpose
Despite our experience, we believe heat pumps are an amazing technology and the future of heating. They can deliver efficient, eco-friendly heating when installed correctly.
Our frustrations and lessons ultimately led to the creation of Renewable Heating Hub and writing two books: Bodge Buster and From Zero to Heat Pump Hero. Without our subpar installation and 2.7 SCOP system, these resource for homeowners wouldn’t exist. Now, we’re on a mission to educate others and help them avoid the mistakes we made.
Final Advice
- Take your time: Investigate and question everything your installer says. If you’re unsure, leave a question on our forums.
- Research thoroughly: Visit completed projects, speak to previous clients and understand the design process.
- Demand transparency: Don’t accept vague answers. Insist on clarity about system design, warranty terms, controls and monitoring options.
- Don’t let anyone rush you into a decision: A properly designed and installed system will keep you warm, save you money and reduce your carbon footprint.
Interesting thread – our system will be 3 years old this winter and we have all of the botch issues that you mention – especially heating costs. It is clear that the install was sur a replacement boiler and we are on a fixed flow rate too. I will buy the book mentioned but wonder if you have a local installer to York you can recommend to review our system from top to bottom. I am struggling to find someone with the capability up here.
Welcome to the forums, @Andrew thornton. Sorry to hear about the challenges you’re facing. While I truly appreciate your interest in my book, it’s designed more as a beginner’s guide to help homeowners understand their systems rather than diagnosing issues from a botched installation.
I don’t personally know any good installers in York, but I can recommend two excellent options in Sheffield who might be willing to make the 90-minute trip. The first is @Damon Blakemore from Blakemore Plumbing and Heating ( http://blakemoreplumbingandheating.co.uk ) and the second is @Lee Brown from IMS Heat Pumps ( https://www.imsheatpumps.co.uk/contact ).
I hope that helps.
PS – what brand heat pump do you have installed?
The article makes sense, especially the Heat Loss calculation. I think that is absolutely crucial. I believe that there are specialists who undertake the work. If you have that in hand, you can use it as the project specification. Better than getting the installer to do their own.
Could I suggest/ask if there could be another selection criteria?
I see many new companies emerging onto the market. Some I have never heard of. I expect that they are regular companies with respectable products, maybe European companies exploring the UK market.
But, I might suggest caution. Mars mentions Warranties. I might suspect that if a company exits the market, even an insurance-backed guarantee might not be very practical. I am thinking worst case, for example a PCB (printed circuit board) fails.
So, I might suggest sticking with only those companies that can show a long track record of being in the ASHP game, in the UK?
Any views on that?
Hello,
Is Global Energy Systems you mention the one based in Lytham St Anne’s? We have an ASHP fitted by them and there’s been so many problems with it + high electricity bills. At our wits end.
Welcome to forums @Andi. Yes, it’s the same company. Please elaborate on your issues, and when was it installed?
Hi, we had our ASHP fitted by Global Energy Systems nearly three years ago and have had several problems from poor installation to repeated breakdowns and high electricity bills. In the winter our bill went over £400 for one month. After reading the first article, it seems we are not the only ones with these issues.
This week an engineer from Global spent more than four hours working on the pump, but we still cannot get the room temperature up to 20 degrees. If anyone knows an engineer who can help, I would really appreciate it.
@brianspranklen, please share more specifics about your issue(s) to see if we can point you in the right direction.
Thank you for your input. We are now in dialog with Global, hopefully things can be sorted? We’ll keep you updated.
@brianspranklen, good luck. Keep us posted. Glad they’re trying to help after seeing your post here.
@Mars I was surprised to read your praise for Mitsubishi for remote connectivity and telephone support for diagnosing problems. Here’s my experience:
I have had a Mitsubishi Ecodan R290 10 kW heat pump since early September. The unit does not come close to meeting Mitsubishi’s published performance specifications.
Actual performance vs Mitsubishi specification:
COP at 35°C flow, 7°C external: 1.4 (spec 5.1)
COP at 35°C flow, 2°C external: 1.2 (spec 3.24)
Noise level at 1 m: 68 dB (spec 47 dB)
My energy bills have doubled and my home is cold. It has had a real impact on our comfort and our life.
What happened when I asked Mitsubishi for help?
Despite reporting the issue on 22 October, Mitsubishi repeatedly delayed, passed responsibility around, and failed to take ownership. Their communication has been slow, contradictory and at times obstructive:
Technical support acknowledged a site visit was needed 10 November, yet Mitsubishi failed to schedule one, then required a “warranty claim number” that their own staff failed to issue.
I repeatedly had to chase, re-explain the issue, and even agreed to pay for the visit upfront just to get progress.
Forms were “lost”.
After weeks, the request was marked “urgent”, but still no visit date.
When the unit finally failed with an error code (P8), Mitsubishi still offered no practical assistance or timeframe.
I also submitted a formal complaint referencing their own ISO9001 obligations. No response.
The heat pump supplied is defective and far outside its published specification.
Mitsubishi’s after-sales support has been unresponsive, disorganised and extremely slow.
We are left with a cold home and extremely high electricity bills.
I expected far better from a company of Mitsubishi’s reputation. Based on my experience, and seeing over 140 other one-star reviews on TrustPilot with similar themes it is hard to see why anyone would select Mitsubishi.
Wow, the disappointed Global Energy Systems customers are emerging at speed. There are a lot of issues in Global’s approach to installs and their lack of design competence.
@brianspranklen, do you remember who the engineer was? Was he from Global Energy Systems?
Where in the country are you based (county)?
This recent cold snap on mine has made we want to rip my heat pump out and go back to living in a cave.
2 years, numerous site visits, nothing changed. I told my installer 2 years ago that’s it’s undersized…. I was talked away from that, but it’s still under…..
@davidnolan22, it’s so frustrating. Sorry to hear that. Have you considered speaking to them again? Is the heat pump generating the heat and it’s the emitters that are not delivering the heat, or is the heat pump just not delivering the required flow temps at all?
What heat pump have you got?
@Mars there is plenty of emmiter capacity. The heat punp ain’t got the puff to get the flow temps required.
@davidnolan22, same old frustrating story. Sorry to hear that. Does the size match your heat loss calcs? If there’s a discrepancy you could escalate on the basis of misselling, and take the matter to one of the consumer codes.
@Mars the size matches the heat loss calc they did. But, they assumed there was some insulation in one floor where there was none. They installed the UFH and told me not to bother insulating it so how that happened is beyond me. That was a 1Kw error. But, there should be enough fat in calculation to still be ok. But it’s not
@davidnolan22
Perhaps you could post some more info about your setup, house and system and WC parameters – you never know it may be possible to diagnose.
Please confirm that are running your heat pump 24*7, the weather compensation curve has been adjusted, and all Thermostats/TRVs are set to max so they have no effect and if there is a mixer on the UFH that has also been set to max?
@JamesPa
I’ve done this last winter somewhere. I got some good advice then.
Nub of it is, I think, poor design between UFH and rads. UFH gets most of the flow and power, rads has to make do with slightly bended flow (small LLH) temp that can only satisfy the UFH. But, and its a big but, its not like the UFH is overheating. it struggles (and does not) get to design temp at 0 degrees, the only way I can get the flow temp up to give a flow the rads might actually produce heat is to cut the UFH flow so much, then they struggle/can’t keep their area warm. They have been out loads, made 2 attempts to improve it, but its made no difference at all. I think, and have always though, the heat loss for whatever reason is wrong. the house needs a bigger heat pump. Its a 260m2 retro fit, that I did a reasonable job insulating, but its by no means amazing. 11.2kw heat pump. 120m2 of 150m2 of the UFH is uninsulated concrete slab that they said was fine as it will be factored in.
But, the next mitshi is a 14kw, that fails the sound assessment. They initially messed up the first design and positioned a heat pump position that failed the sound assessment so we had a last minute change of position that means we have a stupid and hard to get to primary pipe run. That pipe run with 2 pumps on can’t get the flow rate for a bigger heat pump. the electrics are not in place for a bigger heat pump. The would need to rip apart my brand new house that we’ve poured our life saving and mental health into because the installers I used could not do their job properly.
NAPIT I’ve not used yet, but I imagine will be a waste of time.
MCS I imagine too be be a waste of 5 years of my life.
I’ve got a beautiful house in a lovely area that I can’t heat up to what I was promised on an averagely cold day in Sheffield. If I ever had to sell this house, how would I sell it: “here is the heating system, good luck, it works great March to mid November".
The mains gas has been taken out from my house back to the street now, I can’t go back to a heating system that although has faults: worked, i’m no eco warrior, i did not do this to save any planets. I’d love to have a nice 20-25Kw system boiler in my house so I never had to look at the weather forecast 5 days in advice and get stressed about. Humid and cold days….. that’s when I actually start to lose sleep.
rant over.
The last bit of that is bad. Thats just badly (well appallingly) designed UFH and most likely the fundamental problem here – half your energy is going into heating the ground! This of course would also be true with a larger ASHP or boiler!
NAPIT I’ve not used yet, but I imagine will be a waste of time.
MCS I imagine too be be a waste of 5 years of my life.
Judging by what we hear here, yes to both.
You are very lucky, I wish I lived in or near Sheffield, sadly I’m in the South East which is convenient for London and has little else going for it.
Do you know what the temp drop is across the LLH (between flow and flow). Removing it may well help.
What about adding a 3kW backup electric heater. You would only need to use it for a small number of days per year. Maybe you could get away with using it only during cheap tarrif periods (in which case Id be tempted to get a 6kW one – so you can max out).
Another trick is to heat DHW on the immersion in coldest weather so the heating doesnt have to go off for a couple of hours.
Any scope for a bit more insulation – draught exclusioin etc?
It sounds like its marginal so maybe with some tweaking you could get it to the point where it works except on very extreme days
You may already have thought of these however.
@JamesPa
The LLH is above, which typical max flow and return the system gets too.
Taking it out sounds like a plan, but a) I’m no plumber and b) the installer has to think its the right thing to do and want to take it out.
Yeah, the back up heater….. thats a funny one. As may sound like the simplest solution…. but, I didn’t sign up for that. I don’t really want a 3Kw 1:1 heater. and you say the coldest days, yesterday in Sheffield was 0.6 ave temp, and I would have needed the heater for much of the day. Is that really that cold?? I don’t think so. They have already installed me 6 circulation pumps that I have to pay for, I’m not keen to add 60kw to the daily heating bill for any day that is close to zero.
There is no more insulation I can add. I have been so anal about draughts. had the window company come back so many times to readjust just anything if I felt I could feel a draught to check, I’ve been round with silicone gun, you name it I’ve done it. I changed all the bathroom vents to expensive ones that stopped back draughts that cost me £500. After seeing what I went through the builder and Plummers said there reluctant working on another house with a heat pump. They warned me and I should have listened.
OK so feed to rads colder than feed to UFH and colder than flow temp from heat pump. Not good, losing efficiency and thus oomph to building. Taking it out will make a small difference, but maybe not enough to cover the problem.
Your ASHP isnt the problem so far as I can see, the problem is the UFH. Without insulation it was always going to be an expensive madness to push probably 4kW straight into the ground, whatever heating you put on the back end. If your installer was responsible for this then I would tell him to fix it, which involves digging it all up and doing the job properly (or something else, eg compensating you for the stupid build or at least putting in a backup heater FOC.
I presume that turning up the flow temp doesnt work – because the heat pump is already running at max power 24×7.
I just checked degreedays for East Midlands. There were only 11 periods of 24hrs in the last 386days when the average temperature was <1C. Not sure how Sheffield compares to the East Midlands weather station, but I really wouldn’t rule out a backup run eg overnight on cheap rate to charge the slab.
@JamesPa
we did have this discussion during the build. I was quoted 10-15k to dig up all the floors and insulate them, and some were in an old cottage and couldn’t really be done. I had the designer from Ambient come to my house and say not to worry that actually laying on a concrete slap on the ground is better than people imagine and only 6% loss downwards. I watched a video from Urban Plummer which said something similar.
Digging the floors up now is never going to happen.
I can’t turn up the flow, its maxed out at 35-36. I can only get flow up but shutting off parts of the UFH. I might play with this some more. run the floors patchy but hotter. This wont create energy though. Just allow some to get to the rads.
Lets see what happens after their next visit. It apparently just needs setting up better.
fair enough!
Better advice IMHO would be don’t work on a house with uninsulated UFH, or if you do fit radiators instead!
Well thats an admission by the installer then that he is responsible for getting it working! Hold onto that.
I have heard those arguments about UFH heat loss but cant see how the physics supports them (and nobody has yet explained how it would). Perhaps if the UFH pipes are close to the surface and any surface covering is highly conductive then yes. Heat will escape the easiest way it can, and if you put anything faintly insulating on top then the heat is going down not up. Convection doesn’t exist in solids so ‘heat rises’ is not true in this case, it will spread any way it can.
I take it you have solid flooring not carpet, directly bonded to the slab, not sitting on top of an insulating layer.
@JamesPa
yeah, LVT direct to it, very thin profile. maybe 10-15mm on top of pipe
Thats good at least. Is your soil locally damp or dry? Im presuming the floor is something like 100mm slab on hardcore on soil with a DPC somewhere. If the soil is damp it will be damp (and therefore even more heat conductive) up to the DPC
@davidnolan22 Inspired by someone on buildhub I asked ChatGPT and Duck.ai (which uses chatgpt and other LLMs) the following question:
“Suppose I have underfloor heating with pipes at 150mm centres buried 15mm deep into concrete that is 100mm thick, sitting directly on damp soil assumed temp at sufficient depth 10C. Suppose that on top of the concrete is say 5mm of luxury vinyl tile and the room above is at 20C. How much heat goes down and how much goes into the room? You may assume, for simplicity, that the heating continues for several months, that the room is infinite is size and that the pipes are supplied with water at 35C"
They used slightly different methods (which they gave) and both had to make simplifying assumptions (unsurprisingly). ChatGPT assumed a room of infinite area, Duck.AI asked me to specify the room size so I gave it 7m square and 10m square. They gave their methods which look reasonable but I haven’t verified completely (and Im not sure if I will). In summary ChatGPT says 80% of the heat will go down, Duck.ai says 50% will go down. This is at variance with what UrbanPlumber says here, but his somewhat handwaving argument, for which he admits he has no evidence, makes an assumption which I think is incorrect. However your installer may have based his statement on this, its not the first time I have heard it said.
Frankly I don’t know, but I would say that, based on what we have so far, there is at least 50% probability that at least half the heat goes down in an uninsulated UFH arrangement such as yours. If this is correct (and I think you would need to do a finite element simulation to prove it) then it could easily account for your problem.
If you want me to DM you the full conversation with Duck.ai and ChatGPT Im happy to do so. It might be food to ask the exact same question of another LLM that we know doesn’t use ChatGPT at all
@JamesPa
hmmm….. one to ponder.
I’ve no idea how dry or wet the soil is. the old part of the house is from 18th century.
But, I’ve put a 20K floor, 20k kitchen down since then…. we are not digging any floors up…..
Understood. Solutions I can see if you cans somehow squeeze enough out of the heat pump are
Sorry to be the bringer of bad news, but UFH on an uninsulated slab is a massive gamble so far as I can see and, as you say, its not coming up so now the options are limited.
It may be clutching at straws but heat has to go somewhere, is it possible to insulate the external edge of the solid floors so that the whole floor becomes a giant low temperature heat sink? Not ideal but long term would reduce heat loss possibly to a managable level. Soil directly under the floor would gradually warm and reduce heat loss. Maths for this is well above my pay grade but it just might help without digging up the floor.
this has been modelled for the passive house planning package and as a result there are simplified values come out. Heat loss with no insulation under the concrete slab uses a UValue of 2.0 (several variations based on water content level of soil/water table/ whether on a hill & the warmer water runs away etc). When the house has external insulation attached insulating footings too, and dug down to ~0.7m (practical limit) the U value of this ‘heat island’ is 0.7. In either case a lot of heat goes down into the ground not up into the house.
So if you want to use ufh you need to~10-15cm of insulation the minimum is building regs.
You need to insulate the edges and beneath – ‘heat rises’ applies only in fluids not solids, in solids the heat spreads isotopically. If you do this the slab does indeed become a large storage radiator. If you dont you are right that soil underneath will gradually warm, but its likely too large a storage radiator to be useful. I cant do the maths either (I dont think its soluble analytically) but I did ask ChatGPT a question and it estimated (with plausible methodology given) that the time constant for the warming of the soil was order weeks or months. Thus the problem might get better as the season progresses – but isnt particularly practical as a ‘solution’ unless you heat throughout the year.
Understood. Solutions I can see if you cant somehow squeeze enough out of the heat pump are
Sorry to be the bringer of bad news, but UFH on an uninsulated slab is a massive gamble so far as I can see and, as you say, its not coming up so now the options are limited.
If this were my nice house in Sheffield (sorry I’m still envious of the location) I would bite the bullet, go for the first and get a suitable tariff to run it on, or a nice log burner if its permitted where you live.
@JamesPa
We have a wood burner, and use it. But one day they might be banned.
All this is pretty depressing to be honest. During the build we had one window company go bankrupt on us, other issues building control who we paid 4000 to go bankrupt….. This house has killed me
I feel for you. I have never done a major ‘build’ personally but I have done several professionally, and I’m sorry to say that incompetent tradesmen and contractors going bust midway is par for the course. Of course there are good people in the construction industry, but I would estimate it’s at the 50-70% level max. The rest are either incompetent, scammers, lazy & couldn’t care less, or several of the above. Despite never doing a major build I personally lost £5k on a scammy roofer a few years ago.
From what you say your installer guaranteed performance, so you likely have the law on your side. Depending on your appetite for fighting you may be able to use that to your advantage. There are degrees to which you can take this, another individual here has steadfastly refused to let go for a year or more and is, I think, eventually heading for success albeit ar the cost of mych frustration. That’s one approach. Another is to keep that approach in reserve and aim eg for getting some sort of fix, not the perfect one, free. Alternatively just move on and fix it in whatever way is now possible, which is what (in some ways to my shame) i did with the roof. You will need to think about what sits best with you.
Keep posting if you want more suggestions, people here are willing to help!