When we moved into our Derbyshire home in April 2014, it was already a work in progress. The ground floor was insulated and heated with a wet underfloor system, while the upstairs had two heating circuits: one for the two bathrooms and another for the three bedrooms and hallways. Although the house felt a little small for our needs at the time, it came with planning permission for an extension. We began the extension in 2015 and completed it in early 2018, increasing the house size to 450m². The ground floor continued to use underfloor heating, while the five bedrooms and five bathrooms were heated by radiators on separate circuits.
The house is well-insulated, with walls built to modern standards (using thermalite blocks and 100mm insulation) or dry-lined plasterboard inside thick, rendered old walls. The lofts are also well-insulated. However, the 11 exterior doors remain the weakest point in terms of insulation, despite all windows and doors being double-glazed. We also have four solid fuel fires, which we use sparingly during the coldest months of December through February.
Energy Efficiency Challenges
Despite our efforts to keep heating costs manageable (never heating the house above 20C and setting the water temperature to 55C) the running costs were significant. My usual approach was to encourage everyone to “put on a jumper,” tape up the immersion switch, lock down the nine thermostats, and turn the TRVs (thermostatic radiator valves) down to 2 or 3. While our system wasn’t inefficient, it was powered by an LPG boiler (first a Glowworm, then a Vaillant, replaced in 2020). LPG proved expensive and difficult to source, with prices rising steadily. By 2022, the cost per kWh had reached 5p, and it was clear that prices would only continue to climb.
The Turning Point: Embracing Renewable Energy
Our journey toward renewable energy began in 2016 when Octopus Energy took over our failing electricity supplier. Their innovative tariffs made solar panels, batteries, and two-way inverters increasingly attractive. Although I had installed a 4kW solar system in a previous home, the economic case for solar at this property only became viable in early 2023, as panel and battery prices dropped.
Key milestones in our journey include:
- Completing the extension in March 2018.
- Replacing the gas hob with an induction hob in November 2019 for better air quality and ease of use.
- Installing a smart meter in March 2022, enabling 30-minute interval monitoring.
- Transitioning to a full electric vehicle (EV) in September 2022.
- Installing 29 solar panels (10kW peak) and two 5kWh batteries with a two-way inverter in March 2023.
- Moving to the Agile Octopus tariff with export capabilities, despite a challenging process.
- Replacing the front door in August 2023 to improve insulation.
- Flooding during Storm Babet in 2023, which led to replacing 70m² of carpeted floors with stone.
- Replacing the LPG system in January 2025 with two Mitsubishi Ecodan cascade air source heat pumps (17kW total), a new plant room and a hot water tank.
- Adding a third 5kWh battery to optimise low-cost electricity imports and mitigate peak prices.
- Switching to the Cosy Octopus tariff in February 2025.
Energy Usage and Cost Analysis
Our investments in solar panels and air source heat pumps totalled around £30k, with a long payback period anticipated. However, these changes have allowed us to maintain energy costs close to 2022 levels, despite rising prices.
- 2022:
Cost: £3,758 | Usage: 39.7MWh | Average cost: 9.5p/kWh
Heating was heavily used from November to April, with minimal usage from May to September. - 2023:
Cost: £4,253 | Usage: 36.5MWh | Average cost: 11.7p/kWh
The installation of solar panels and batteries reduced net usage from 10.7MWh to 7.5MWh. Time-of-use tariffs were exploited in Q4. - 2024:
Cost: £3,020 | Usage: 30.6MWh | Average cost: 9.9p/kWh
Batteries and solar panels helped absorb price inflation, with net electricity imports dropping to 1.5MWh. - 2025 (so far):
Cost: £880 | Usage: 5.3MWh | Average cost: 16.7p/kWh
Target: 12MWh (COP 3) at 12p/kWh. Energy usage in January and February has significantly reduced compared to previous years.
Key Takeaways and Lessons Learned
Our journey has been a steep learning curve, with several unexpected challenges and valuable lessons:
- ASHP Performance: I knew that running an air source heat pump would differ from a gas boiler’s on-off cycling, but I underestimated the complexity of a cascade system. The ASHP struggles to heat the house from zero to 20°C, and defrost cycles every 40 minutes reduce efficiency during freezing conditions. Installing an ASHP in frosty weather is not ideal.
- Frost Damage: I didn’t anticipate frost damage to the concrete plinth under the ASHP, which now needs to be redone.
- Air Quality and Circulation: Constant temperatures led to mustiness, as the gas system’s heating and cooling cycles had previously forced more thermodynamic circulation. We now leave internal doors open to encourage airflow and often open windows during good weather to improve air quality. This has prompted us to consider installing an internal air circulation system.
- Thermostats and TRVs: I hadn’t fully grasped that thermostats and TRVs now act as limiters rather than controllers. They switch off if temperatures exceed 22°C, and the system runs on weather compensation, aiming for 20°C.
- Monitoring Challenges: Measuring consumption or COP with a cascade system is difficult, as neither the MELCloud app nor the control panel provides accurate data. I now estimate based on the Solar app, assuming my non-ASHP electrical load in 2025 matches 2024. Thankfully, the Sunsynk app is excellent; without it, I’d be lost.
How the Renewable Heating Hub Forum Helped
The Renewable Heating Hub forums were invaluable in troubleshooting and optimising our system:
- Heat Transfer Issues: I learned that a release valve pumps heat back outside if the system encounters too much friction (e.g., closed or blocked valves). This explained why we were generating heat that wasn’t transferring to the house – effectively heating Derbyshire in January!
- System Settings: The initial setup had the hot water and heating temperatures set too high, causing repeated cycling. Weather compensation wasn’t enabled during installation, but forum advice helped me adjust the settings for better efficiency.
- UFH Valve Fix: With confidence gained from the forum, I manually released a stuck underfloor heating (UFH) valve using a radiator key. The rush of water into the circuit was a moment of elation and relief, saving us the cost of draining and clearing the system.
- Encouragement to Meddle: The forum gave me the confidence to tinker with the system, which has been crucial in resolving several issues.
The Installation Process: A Mixed Experience
The installation of the air source heat pump and associated systems was a mixed bag, with both positive and negative aspects.
The Good:
- The plumbing quality is good, and the system works well after some adjustments.
- I believe the COP is favourable, though accurate measurement remains challenging.
The Bad:
- Poor Insulation: The pipe insulation was subpar, and I had to redo most of it myself.
- Faulty Equipment: One of the Ecodan units was faulty out of the box and had to be replaced. The installers initially dismissed our concerns but eventually confirmed the fault.
- Installation Errors: A pump valve was left closed during commissioning, preventing heat from circulating in January. I discovered and fixed this myself.
- Workmanship Issues: The installers repeatedly left doors open in freezing weather, used crowbars to rip up floors, and left holes under carpets. Woodwork and wiring were poorly executed, with control units installed too close to door jambs, preventing doors from closing.
- Commissioning Failures: No proper commissioning or training was provided, and we were simply told “not to meddle.”
- Battery Delays: The incorrect battery was delivered initially, and it took a month to source the correct one. The leads were too short, adding further delays.
- LPG Tank Removal: I hadn’t factored in the £1,000 + VAT cost to remove Calor’s buried LPG tank from our front lawn.
Looking Ahead
Despite the challenges, our journey has been rewarding. The system is now operational, and we’ve significantly reduced our energy costs and environmental impact. However, the installation process highlighted the importance of thorough planning, skilled workmanship, and accurate monitoring. Future improvements may include enhancing air circulation systems and further optimising settings to maximise efficiency.
While the road hasn’t been smooth, we’re proud to have transformed our home into a more sustainable and energy-efficient space. The lessons learned (and the support from the Renewable Heating Hub forums) have been invaluable in navigating this complex but worthwhile journey.
Incredibly detailed piece @Carpenterstation – thanks for sharing your journey, and we’re thrilled that the forums helped you get a better understanding of your system!
Great post. I installed an ashp last year and while the house is now nice and warm for my elderly parents, i cannot say it was a good experience. The workmanship was not very good, one radiator was placed too close to a door and had to be moved, there was no effort to run pipes tidily in the attic within the insulation, they go all over the place, on top of each other and the attic insulation. The pipe insulation does not appear to be very good with a thermal camera showing lots of heat loss. One switch was left closed which meant no hot water for several days, the wifi unit often failed to connect to the thermostat and we were told to ‘not touch anything’ dispite not being given any explanation. Overall we had to call back the company several times, and even the temperatures were not left correctly, as thats the job of the commissioning engineer who didnt arrive for 3 weeks! This was in November!
The outdoor unit dripped water and had to be re-leveled to stop the damp. We had to re-pressurise the system several times, before we saw water dripping from one of the filters.
And to cap it all, i have been unable to find anyone to service the system annually, which we have to do for the warranty, apart from the installing company who want £300 a year! so any money we save on heating efficiancies, we have lost for the increase in servicing.
So while it does now work, i do not know if we could make it more efficient, is the weather compensation working, and the whole experience has left us feeling very let down. We need to replace the boiler in our own house and we are going for a gas boiler. Because of the experience at my parents house and also due to the high cost of installation and ongoing servicing costs.
I agree with the cost of servicing being a major disincentive for the heat pump purchase. I had hoped that investing in a heat pump and associated radiator changes would provide the benefit of lower running costs. This will be the case in terms of the energy cost but the overall saving will be wiped out by the annual serviving cost. We all have to hope that an increase in the number of people who are competent in heat pump maintenance will substantially bring down the service cost. If not, there will be increasing difficulty with persuading people to change to heat pumps as word spreads about the high cost of servicing.
@JohnR The really annoying thing about the high service costs is that servicing a heat pump is a lot less hassle than a gas boiler. All that is required really is check for debris around the outside unit, clean any filters and check the antifreeze levels (if you use it) I ran and serviced my last heat pump for 12 years with no issues till I sold the house.
Does anyone get their fridge serviced annually!
@bontwoody, I completely agree with you. I’ve said this many times before as well. In our case, Global Energy Services charged us £216 for a service, which is just crazy. In comparison, our oil boiler service cost £70, and the technician took it apart, cleaned it, tested it and did everything needed, all in the same amount of time. The difference in cost is completely disproportionate. This is something that the industry needs to address and I will start hammering this point in my podcasts and interactions with the industry. It’s not fair.
@Mars It really just is a case of greed and easy money I fear, Mars
@Mars I completely agree. When our ASHP was installed, I read the servicing checklist, and it’s a lot of inspect this and check that, and not that much of actual doing anything. About the only thing I can’t do myself is check the refrigerant levels. Has anyone actually had their refrigerant levels checked (and topped up as required) during a service?
Nope.
If you have access to the backend of your heat pump control panel, you can do this by doing some maths that will tell if you are potentially running low on refrigerant. Our levels were never checked, but they did make a flying assumption a few months ago though:
Heat Pump Defrost Error? How to Rule Out Refrigerant Issues!
I feel that this is a good campaign for me to embark and ruffle some industry feathers. Please cast a vote in this thread so I can build up some ammunition: https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/heat-pump-servicing-maintenance-good-value-or-rip-off#post-32403
I’m still to come across a heat pump service that’s below £200.
@Carpenterstation
Who did your ASHP install? Are they a local Derbyshire firm and would you recommend them to take over the annual servicing of my ASHP?
I don’t do recommendations on principle. The firm is based in Worksop or Doncaster I believe, and really friendly knowledgeable folk. But I won’t publish their name on this forum.
Most of the install issues I have relate to apprentices or inexperienced folk learning the ropes – but the boss and his immediate team seem to know a lot.
I don’t know whether they would be willing to service your system. I guess that would depend on location and the model of heat pump you have? (Ours is Mitsubishi Ecodan)
@Carpenterstation
That’s helpful, thank you.
The details of my ASHP are in my signature.