I am not a green evangelist, and I am certainly not motivated by net zero.
Much of the rhetoric around domestic decarbonisation strikes me as overblown and disconnected from how people actually live in their homes. My decision to replace my heating system was entirely practical. I wanted to remove ageing microbore pipework before it failed and the Boiler Upgrade Scheme made doing so financially viable.
The journey to an air source heat pump started with my elderly mother’s house. She lives in a 1980s property that still had its original floor-mounted gas boiler, single radiators and 10mm microbore pipework. In 2023 we began to notice signs of damp appearing from beneath the concrete floor. It didn’t take long to conclude that the pipes were leaking. The only sensible solution was a full replacement of the heating system. That involved installing a new combination boiler, replacing all the radiators and upgrading the pipework to 15mm throughout. The total cost came in at around £8,500.
That experience focused my mind. My own house is of a similar age. Although I had a newer boiler and radiators, the system still relied on 8mm microbore pipework. I had always been wary of it and knew that when it eventually failed, the disruption would be significant. Having just seen what was involved at my mother’s house, we decided to act proactively and replace the system at a time of our choosing rather than waiting for a failure.
Around the same time, I had been following the increasingly polarised public debate around heat pumps. Every newspaper article seemed to trigger knee-jerk reactions declaring them either the future of heating or an unworkable disaster. Buried among the noise were occasional, more measured voices pointing out that heat pumps could work extremely well when properly designed and installed. That caveat interested me. I began watching YouTube videos to understand the fundamentals rather than relying on headlines.
Eventually, I asked Heat Geek to carry out a heat loss survey and provide a quotation. Their proposal was clear and detailed: a 7kW Vaillant air source heat pump, eleven replacement radiators, a new Vaillant hot water cylinder, new controls and integration with the Vaillant online system. The quoted cost was £18,000, reduced to £10,500 after applying the £7,500 Boiler Upgrade Scheme grant. Importantly, the quote came with a performance guarantee.
If the system failed to work as designed within the first two years, they committed to upgrading whatever was required. Compared to the £8,500 cost of a basic gas replacement at my mother’s house, this felt like a reasonable premium for an entirely new system.
To qualify for the grant, I needed an EPC. This rated the house as a D, but also concluded (somewhat implausibly) that we needed roughly twice as much energy to heat the property as we had ever historically used. As the house has a loft conversion, there is no realistic opportunity to add further roof insulation, highlighting how blunt EPC assessments can be in practice.
The installation took place in the summer of 2024. All the pipework was upgraded and the system pressurised, which allowed us to remove the negative-pressure shower pump feeding the loft conversion, an unexpected but welcome improvement. The Vaillant hot water cylinder is so well insulated that the airing cupboard has effectively stopped functioning as a place to dry clothes, which neatly illustrates how much heat modern systems no longer waste.
The system has now been running for almost two full winters and has performed well. Vaillant’s manuals are not written with homeowners in mind, but with some effort I worked out which settings needed adjusting to suit our house across seasons. In winter, the heating runs continuously at a steady 19C, maintaining a consistently comfortable temperature throughout the house. In summer, the system only heats domestic hot water once a day, at 1pm, to 55C. That single cycle provides more than enough hot water for normal daily use.
Over the past twelve months, the system has delivered a SCOP of 4.17 for space heating, and a combined SCOP of around 4 when hot water is included. Those figures are not theoretical; they are based on actual usage.
Ahead of the installation, I switched energy supplier to take advantage of OVO Energy’s Heat Pump Plus tariff, which offered electricity at 15p per kWh. The rebates were worth around £350 last year, but the tariff is being withdrawn at the end of January 2026. From what I can see, none of the currently available time-of-use tariffs will allow the system to run as cheaply or as simply. Going forward, my heating costs will likely be comparable to gas, but with the benefit of an entirely new system and a consistently warm house.
Living with a heat pump does require a degree of engagement. The main thermostat is by the front door and remains set to 19C at all times. I keep a small thermometer in the sitting room, which helps me spot when the system begins to struggle as outdoor temperatures fall. That acts as a prompt to make small adjustments to the heat curve. It’s not onerous, but it is different from gas boiler ownership.
There is also a small gauze filter in the airing cupboard (about the size of a thimble) that has a significant impact on system performance. If it becomes clogged, the flow rate drops and the heat pump can shut down. My system runs at around 1,200 litres per hour. If that falls to 1,000, I clean the filter under the tap. On one occasion it became damaged, and sourcing a replacement proved surprisingly difficult. There are multiple designs, and they are not interchangeable, a point that installers and manufacturers could do more to address.
Once the installation was complete, we removed our final gas appliance (an old Parkinson Cowan cooker) and replaced it with an electric oven, an induction hob and an air fryer. The gas meter was removed, making the house fully electric.
Before the work, our combined annual gas and electricity consumption was around 18,000 kWh. Last year, our total electricity use was 5,812 kWh. That stark reduction in energy consumption highlighted just how inefficient the old gas boiler had been at the point of use.
Politically, there has been much talk of accelerating heat pump adoption, with targets of 600,000 installations per year and proposals to rebalance environmental levies between gas and electricity. So far, progress has been underwhelming. Installations remain far below target, and while there is talk of shifting some levies into general taxation from April 2026, meaningful rebalancing has yet to materialise. Given that most households use both gas and electricity, there is a strong case that such changes could be broadly cost neutral while making electricity (and therefore heat pumps) more affordable.
For me, this was never an ideological choice. It was a pragmatic decision driven by ageing infrastructure, cost transparency and timing. With a competent design, a proper installation and realistic expectations, an air source heat pump has proven to be a reliable and effective replacement for my old gas system.
Thank you for sharing and glad to hear you are happy and it works as you expected.
I also have a Vaillant (gas boiler) and I agree the manuals tend to have that viewpoint of what the kit is and what it can do and not how it can do what the user wants!
Impressive to see a scop of 4.17, as from reading RHH, it would seem most installers treat that as a theoretical maximum and leave the site as quickly as they can.
Having a performance guarantee must have made all the difference.
You are not alone being impacted by OVO stopping their heat pump tariff. A few people posted here about it.
One “solution", (that comes with some additional expense) is to add the ability to purchase electricity at the lowest rate and use it when your tariff expensive. BESS systems can help and depending on whether you are happy to restrict yourself to a tariff allowing a few periods of cheap charge a day or a single overnight, you may need less or more capacity. There are a few threads here on that, this is one.
It may be fair that installers are putting focus on the thermal efficiency of the pump but financial performance would always surface at some point!
@Robert M Thank you for sharing this as its always nice to hear good news stories.
Your numbers (energy consumption before and after and SCOP) are remarkably similar to mine and I suspect this may be the case for your installation also. I have had my heat pump, also a Vaillant, for only a year but can say with certainty that its been a success. That gauze filter which, in my case is located behind the heat pump (even the guy who installed it cursed when he was forced to lie down to undo it the first time it needed cleaning, which was the first time I knew it existed) is indeed a bit of a pain, but I think all heat pumps have, or at least should have, one because it protects the heat exchanger from clogging up. I suspect that this is true of boilers as well which also feature heat exchangers that have notoriously narrow passages.
In terms of comfort my house is the best ever by a significant margin. Prior to getting a heat pump I turned our boiler temperature down to the minimum it could reach (as compared to the 75C that it had been left at) which was a worthwhile improvement, but the heat pump with weather compensation has taken it to another level.
The only comment I would make about your setup is – have you tried using yours without an active thermostat (ie with the thermostat turned up to max). I find mine works best (most comfortable) with absolutely no room influence at all except at the very ends of the season, when solar gain dominates heat loss. At this point I switch from ‘room mod inactive’ to ‘room mod expanded’, which essentially means that the temperature measured by the Sensocomfort acts as a limiter. Obviously this will vary from house to house so whatever suits you best (given you have a good SCOP) is the best approach.
FWIW I have an electric car and find an EV tariff works well also for the heat pump. I could do better still if I programmed a ‘set forward’ (ie increased flow temp) at night, which I currently don’t. However I do run DHW at night and of course the weekly legionella cycle.
Once again thank you for sharing your experience. My guess is that most people who are happy just get on with their lives and, as a result, we typically hear about the failures; its good to balance that with the successes.
Thank you for your post @Robert M , not only an interesting read but encouraging words for those of us just starting out on the journey of updating our household energy infrastructure.
Having recently moved into a property where the oil boiler failed, BER, in week two, the learning curve has been steep. We had hoped to run a year, or two, on oil and plan for an ASHP and solar with less expedience.
However, heating being provided by various means plugged into 13A sockets in mid-wintet does focus the mind; … almost literally, “All hands to the (heat) pump".
Ironically we have spent most every dry daylight hour outside, ‘attacking’ a garden neglected for over a decade …. it’s unsuprising how a bit of exercise can keep one warm ! That, and plenty of layer-wear indoors.
In short order we have also “crammed" our knowledge-base to speak some “lingo bingo" ; a dialect of heat-pump, solar and battery; and also chosen installers for the household heating and PV systems.
PV is being installed in late Feb. The ASHP goes in mid- April, which requires a re-plumb to remove u-bore, install UFH downstairs, and new rads upstairs.
Both install companies are busy people (hopefully a good sign). The PV/Battery early install date was a bit of luck due to a postponed job. That, and I think the surveyor had some sympathy for us, having gone back to his van for his puffa-jacket and beany, when he visited during the cold-snap several weeks ago.
Battery energy should take some of the financial sting out of relying upon 13A heating appliances. A nod here too to Octopus for installing our smart-meter in very short order. We had been advised a 3 month wait; but explaining our situation had our request expedited. Unfortunately, their heat pump survey and system spec did not quite meet our expectations.
Our main reliable resources have been: Renewable Heating Hub (forum, books, YT channel, & Podcast;); and Gary Does Solar (YT channel and Patreon Utilities).