Hi everyone, I'm new here, but after a discussion with @editor, I thought I’d share my experience of having an ASHP installed by British Gas.

After buying a 1956 three-bed semi in a small town northwest of London, saying we had a small project on our hands was an understatement. Everything needed updating, including the heating, which at the time was a gas boiler that was around 20 years old.

The property had been a rental for the past 10-15 years. The owner had crammed everything from the garage into the house, including shockingly oversized or undersized, mismatched radiators that desperately needed replacing.

A few months later, I started making some calls to get quotes to replace our long-overdue heating system, including the pipework and radiators. This was at the beginning of 2023, and there still wasn’t much information available about ASHPs in general.

As far as I know, British Gas was one of the first to advertise and offer installations, including handling the government grant, which at the time was £5000. After some research, it became clear that we needed to improve the insulation and draught-proof the house to get the most out of the ASHP.

Luckily, this was part of the plan from the start:

• We had well-insulated cavity walls.
• The old, draughty double-glazed windows were replaced with triple glazing, including cavity closers and insulation around the frames.
• External doors were replaced with highly insulated ones.
• We replaced the old, poorly installed (compressed) 100mm loft insulation with 300mm.
• We replaced the old loft hatch with a custom-made one with 100mm insulation and seals.

After receiving a few quotes to replace our gas system, it became clear that the costs were similar to installing an Air Source Heat Pump after deducting the £5000 government grant.

Yes, I know people might say we shouldn’t have gone with British Gas in the first place, but at the time I hadn’t heard of Heat Geeks. I couldn’t find a single local company offering ASHP installations, and British Gas offered to handle everything, including the grant application, so we went for it.

Surveyor Visit – Heat Loss Calculations

The surveyor’s visit lasted almost  around 6 hours, which was reassuring, as it felt like the calculations were done thoroughly. At the time, we still had the old windows and doors, but we informed the surveyor of our plans to replace them to improve the insulation of the house. Once we received the calculations, the SCOP in the report came out at 5.04 at -2.34°C with a 45°C flow temperature.

I didn’t know what these figures meant at the time, but the surveyor assured me they were good. The original quotation and heat loss calculations were based on a 4kW Daikin model, and the price was much higher than we had anticipated. It wasn’t until I asked if there were any other options that I was told we could go with the Vaillant Arotherm Plus 5kW model.

The original quote for the Daikin was for a 4kW pump, and I was told the Vaillant option wasn’t offered earlier because Vaillant doesn’t have a 4kW model in their range.

I figured it was worth getting a slightly oversized pump, especially considering the £5000 price difference between the Daikin and Vaillant units. For me, it was a no-brainer, and after doing some research, I was confident the 1kW difference wouldn’t negatively affect the system’s performance.

So, we decided to go for it.

By the way, our decision wasn’t based on the belief that ASHPs would save us money. I had done my research, and I was content with the fact that heating our home with ASHP might cost the same or even slightly more than with our existing heating. We went ahead because, in my mind, this is the future, and the low flow temperature would give us a nice, even heat distribution throughout the house. We also liked the idea of using renewable energy and no longer needing a gas supply to our home.

Installation Planning

There was no consultation to plan the installation.

We had concerns about where the pipes were going to run. I had hoped someone would visit to discuss this, in case something needed moving to make space for the pipes. This never happened, and we ended up with pipes running from our utility room, where the pump equipment is installed, into the house with intricate 90-degree bends just to avoid a small fuse box that was in the way.

This could easily have been moved (remember, at this point, I already had my own electrician, and moving the box wasn’t an issue, as long as I had known about it).

Delivery Day

All the equipment, apart from the heat pump itself, was delivered by a British Gas driver on a rainy day.

The problem arose immediately.

We don’t have a driveway, so all the equipment had to be moved closer to our garden gate. The issue was that it then needed to be moved to the back of the house, or even into the house, not only to protect it from the rain but also from the risk of theft.

Much of it looked expensive, and you could clearly see the radiators and other costly-looking parts required for the installation.

The problem was that some of the larger radiators weighed over 60kg, and I was on my own. The driver refused to help me due to his insurance policy (rightly so) and even called his supervisor to complain that the customer had no help to unload and move over 1000 pounds (500kg) of equipment.

As I mentioned, all this took place on a rainy day, so everything got soaked, including the electronics that, at the time, I had no idea were there.

Heat Force Engineers Arrival

Between the heat loss calculations and other correspondence, I was notified that the installation would be carried out by contractors, not British Gas engineers. I didn’t give it much thought at the time and had no concerns, but when two HeatForce engineers arrived, having travelled all the way from Bristol, which is 150 miles from where we live, I became a bit worried.

Right from the start, the two engineers complained and swore at each other for being sent all this way to install a system they’d never worked on before. They did this right in front of me without hesitation or concern.

This raised a red flag for me, but it was too late—we were committed by then, with no way of cancelling.

The installation took a week, and during that time, everything seemed to be going according to plan.

Configuration of Vaillant SensoComfort Controller

At this stage, I still had very limited knowledge of how to configure the controller for my new heat pump. I had hoped all my questions would be answered by the two engineers installing the unit, but I was very wrong.

When the time came, they asked me if I knew how to turn on the screen of the SensoComfort controller, which was already mounted on my living room wall.

This was not a good sign.

I didn’t want to show my disbelief and shock, as I wasn’t sure how they’d react, considering they were already annoyed at being sent 150 miles to do this job in the first place.

It became clear they had no idea what they were doing, and eventually, we ended up watching a YouTube video on how to configure the unit. I knew that every setup is different and that the settings should be tailored to the specific configuration, but at that moment, this was our only option.

I’m not sure if this is still the case, but back then, SensoComfort units were preconfigured by default for gas heating systems. As I later discovered, the flow temperature was still set to 60°C, which is standard for gas heating systems.

Mismatched Radiators

Long before the installation took place, I had hoped someone from British Gas would contact us to discuss radiator placement and selection. After all, I wanted to have some control over what was installed in our home.

Unfortunately, as I quickly found out, that didn’t happen.

The radiators arrived, and to my surprise, two of the vertical radiators that were supposed to be fitted in the living room were dramatically mismatched in size.

One had 6 sections, and the other had 10.

You might think I’m being picky, but honestly, the larger one looked awful. It’s only a small three-bed house with a modest-sized living room, and that one radiator was taking up nearly a third of the wall space!

I called British Gas to question their selection of radiators. I was told that the choice was based on the heat loss calculations, and that this is what I was getting. I pointed out that surely we could get two vertical radiators with an equal number of panels, but I was told that this wasn’t possible.

Frustrated, I hung up.

Luckily, I had an invoice for everything that was purchased for the installation, and most importantly, I knew where it was purchased from. I went on the radiator supplier’s website and immediately found that there were plenty of options available for this specific type of radiator that would still match the output.

Existing Radiators:

To illustrate the issue with the radiators in our living room, which were mismatched, a more symmetrical choice could have provided the same energy output, but with a much better visual result.

Proposed Radiators:

Now, let’s consider a more symmetrical setup by selecting two 8-panel radiators. This arrangement would not only be more aesthetically pleasing and a better fit for the wall, but it would also deliver the same heat output.

I took a screenshot and sent it to the most incompetent person I had spoken to at British Gas.

A few days later, they came back to me, admitting I was right, and agreed to replace the radiator with ones that had equal numbers of panels—8 and 8 panels each, matching the heat output.

I won’t even mention that we had anthracite radiators in mind, which were available from the supplier, but we weren’t even asked about this option. British Gas just assumed we’d go with the white ones.

Spacing the radiators with off-cuts

It was also ridiculous that the installers used off-cuts of copper pipes as spacers when they realised the pipes behind the radiators were too close to fit them on the wall. This again highlights the lack of planning and the silly solutions they came up with as the installation progressed.

If I’d known this was going to be an issue, I would have sourced some proper, purpose-made spacers.

First Testing

After an hour or so fiddling with the controller, the engineers were ready to test the system.

As it was the middle of May, we started by testing the DHW (domestic hot water). It turned out the system wouldn’t start. After a few calls to Vaillant and trying to decipher the installation diagram provided, they discovered an additional valve had been installed, which wasn’t necessary.

A few hours later, we had another go at testing the system. This time it started up, but the engineers had no idea how to test the heating. Since the DHW was working, they simply assumed the heating would also work.

Handover (or lack of it)

Apparently, during the handover, the customer should be able to ask all the questions they need to safely and efficiently operate the system. I say “apparently” because I had no handover whatsoever.

As you’ll recall, all the equipment was delivered during a storm and was completely soaked, including all the paperwork. After seeing the engineers watching YouTube on my TV to figure out how to configure the Sensocomfort controller, I didn’t even bother asking them any questions about it.

I just realised I’d have to learn it myself.

They handed me the soaked paperwork and left.

As I later found out from my electrician, who rewired the whole house, I was also missing the electrical certificate and test results for the new fuse box that was installed by the Heat Force electrician.

First Failure

It took only a few days for the system to fail due to low system pressure.

The manual gauge was showing 1.5 bar, while the digital one on the VWZ AI interface module showed 0.9 at best, which triggered an immediate error. At this point, I contacted British Gas, as I was told to do in this situation.

Immediately, I was thrown into a loop of being redirected and contacting different people. I don’t even want to count the number of emails and people I had to speak with, but I think it was close to 10 different contacts. Each new person needed the whole story explained again to understand the issue.

British Gas - HeatForce Incompetence

During one call, I complained that the system hadn’t been flushed after installation and that this might be the reason for the drop in system pressure. I was immediately told by one of the British Gas managers I was dealing with that this was definitely not the case.

Surprised by this, I pointed out that it’s good practice to flush a new system to remove post-installation debris, such as bits of copper pipe, dust, and residual soldering paste, only to be told again that it wasn’t necessary and wasn’t the cause of the problem.

It took a few more days for HeatForce engineers to arrive (remember, they’re based in Cardiff, 150 miles away). This time, it was a different team, not the ones who installed the system. After a few hours of investigation, they concluded that the strainer needed cleaning, only to discover that the previous team hadn’t installed isolation valves.

Without these, the entire system had to be drained just to check the strainer.

I was told someone else would come to install the valves and clean the strainer afterwards. A few days later, another HeatForce engineer arrived to install the isolation valves and clean the strainer. To my surprise, he told me straight away that he knew nothing about heat pumps and had only come to install the valves and sort out the strainer.

A few hours later, the valves were installed, and as I had suggested during my conversation with the British Gas service manager, the strainer was indeed blocked. Finally, the system started working again.

Second Failure

Just a few days later, the same problem occurred: low system pressure error. By that stage, I already knew what was causing the issue, so this time I called HeatForce directly, as I’d had no luck with British Gas and had wasted hours being passed from one person to another.

I also pushed the engineers to perform a system flush, as it was clear this was the main cause of the strainer becoming blocked. After all that was done, the system was back up and running.

System Misconfiguration

I must say, it was really tough at the beginning to get my head around all the options in the Sensocomfort controller.

And yes, many of you will say I shouldn’t have touched the installer menu (the one that requires a code), but remember, I had completely incompetent installers who watched a YouTube video to figure out how to set it up in the first place. Eventually, I began to understand the settings and how they interacted.

Back in early 2023, there weren’t many resources available on the subject, so I had to literally follow the manual, Google the technical terms used, and try various configurations, making notes of the previous settings as I went. On top of that, Vaillant certainly doesn’t make it easy—their menus are confusing, with relevant settings scattered all over the place, including those that rely on other settings.

This is far from a user-friendly menu design.

After a few weeks, I finally managed to optimise the system as much as possible with a much lower flow temperature, fully weather compensated, with a heat curve of 0.4 (still tweaking 😊), and a legionella cycle (which I wasn’t told about—although I only run it once every three months or so).

Hardware Issues

Immediately after the installers left, I started inspecting the quality of their work and noticed some serious problems.

Insulation of External Pipework (or Lack of It)

The insulation used to cover the external pipes was not only poorly installed, but it was also not fit for purpose (it wasn’t weather- or waterproof) and far too thin. It was only about 10 to 15mm thick and barely wrapped around the pipes, with many sections left exposed to the elements.

Loose External Pipe Fittings

The pipes were installed on top of 100mm external wall insulation, and since the engineers hadn’t inspected the site beforehand, they used whatever fittings they had to try and attach the pipes to that surface.

I had warned them about this issue and even showed them a few specialised fittings they could have used, but they opted to go with what they already had, leaving the entire external piping supported only by the opening in the wall and flexi hoses attached directly to the pump.

External Pipes Corrosion

The external pipes began to corrode almost immediately. After just three months (and remember, this was still summer 2023), both antifreeze valves were heavily corroded, and it was hard to believe they were meant to last another 10 to 15 years.

I spent countless hours discussing my complaints with British Gas, only to be redirected to yet another manager.

Flexible Insulated Connection Pipes

Since I knew nothing about heat pumps or plumbing, I sought advice from Facebook groups.

It didn’t take long for me to realise how bad the installation was after posting a few photos. Apart from the appalling insulation and corrosion, I was quickly informed that the flexi hoses connecting the external pipes to the heat pump were installed incorrectly.

In the unlikely event of very low temperatures and system failure, where the antifreeze valves would need to open to drain water from the system and protect the pump from freezing, the flexi hoses in my system were too long and installed in the wrong vertical orientation.

In the scenario I described, water would remain in the heat pump, potentially damaging it when it froze.

Once again, I spent ages going back and forth with British Gas. By this time, I was completely drained mentally, trying to manage my work while making endless phone calls and sending emails.

Vaillant Independent Inspection

At some point, I’d had enough and requested an independent inspection from Vaillant, insisting that British Gas pay for it.

After weeks of waiting, I called Vaillant, only to discover that the request submitted by British Gas was incomplete, and I would have to pay for the visit myself. Once again, I was stuck going back and forth between Vaillant and British Gas, but eventually, I had a Vaillant engineer visit scheduled and British Gas happy to pay for it.

The day arrived, and the Vaillant engineer showed up at my door.

Red flags popped up immediately. As far as I can remember, he spent most of the time boasting about his years of experience as a gas heating engineer, barely mentioning any expertise with heat pumps. It’s just my suspicion, but I believe he’d only had a few training sessions from Vaillant before being sent out as an ASHP engineer.

He spent most of the time in my laundry room, drinking coffee and talking about his gas heating career. After about 40 minutes, he handed me a piece of paper with a note that the external temperature sensor should be repositioned to a more sun-exposed area, and off he went.

He never mentioned the questionable insulation, the corroded antifreeze valves, the overly bent flexi hoses, or the incorrect orientation that could have resulted in catastrophic failure of the unit. Nor did he mention the incorrectly installed non-return valve (which I later discovered).

In this guy’s eyes, the system was perfect, except for the minor issue with the temperature sensor.

As you can imagine, I lost all confidence in getting the system repaired, let alone working at the efficiency it was designed for. But how could I question a Vaillant engineer’s knowledge and expertise?

The whole experience was a joke, and it exposed how the entire industry suffers from a systemic lack of training, common sense, and self-respect when it comes to their work.

MCS Certification is a Joke

The MCS certification system is a joke too.

All the engineers who “fitted” our Air Source Heat Pump were supposedly MCS certified.

To me, and many others, MCS seems like a money-making scheme and nothing close to the description below:

           “MCS is a mark of quality. Membership of MCS demonstrates adherence to recognised industry standards, highlighting quality, competency, and compliance.”

How can a job that is self-certified by incompetent engineers be described as high quality, simply because the company performing the work is MCS certified? It boggles the mind.

Official Complaint to MCS About the Quality of Work

I filed a complaint through the MCS website regarding the poor quality of work done by British Gas and HeatForce, only to be told to deal with the companies directly to sort out the issues I had.

PrimaryPro Offer for External Pipework Issue

At some point, after posting about my experience on Facebook, I was contacted by someone affiliated with PrimaryPro, a company that produces waterproof insulation and piping hardware specifically designed for heat pumps.

In exchange for before-and-after photos and videos that they could use, I was offered a complete replacement of the external piping with a new PrimaryPro insulation and new valves, with only the labour cost to pay.

This complicated my situation with British Gas, as I was still in discussions with them about how to remedy the issues. As you can imagine, I was already on edge with them, and eventually, when British Gas offered to take care of the external piping, I declined the offer, opting instead for PrimaryPro, even though I had to pay for the labour costs.

It was a hard decision, but you have to remember that I no longer wanted to deal with British Gas’s incompetence. They kept sending the same HeatForce engineers who had caused the problems in the first place. You can imagine the awkwardness when I opened the door and saw the same engineer who had messed things up initially.

PrimaryPro – Never Showed Up

When I was first contacted by PrimaryPro, it was already late autumn.

We decided to wait for better weather, as the materials they used to make the insulation waterproof required dry conditions to cure properly. Months passed, and eventually, I restarted the conversation about setting a date for the job. We agreed on a date, and I booked a holiday from work, only to find that the guy didn’t show up.

After a brief chat, we waited for another suitable weather window, but that day never came. Eventually, the person behind PrimaryPro stopped responding, and the contact ceased altogether.

At this point, I didn’t know what to do. I had burned my bridge with British Gas and had no idea how to proceed.

Leaky Valve and Destroyed Radiator

Some other problems started to arise. I discovered a leaky, heavily corroded valve in the internal pipework.

Around the same time, I noticed a large, rusty spot on the tiled floor just below one of the radiators. Water was dripping from the top screw of the radiator, and to my surprise, the radiator was so heavily corroded in that spot that it had literally torn apart the thread where the threaded cap was screwed on.

There was a significant amount of rust everywhere—on the floor and the radiator itself.

I was shocked to see such extensive corrosion, especially since I inspect the system at least once a month. I quickly concluded that the flushing cleaner (I believe it was Fernox) might not have been fully flushed out.

As far as I remember (correct me on this if I'm wrong), this product is highly corrosive, which could explain the damage.

Now, I also had a destroyed radiator that needed to be replaced.

Unexpected Call from HeatForce

In the middle of summer 2024, I was suddenly and unexpectedly contacted by HeatForce. They told me they had seen my negative review of their company on Google and wanted to fix the problems I had described in exchange for removing the review.

I was told that the company’s management had changed, and they were working hard to contact all customers who had experienced issues with their work and offering to resolve them.

Without much hesitation, I agreed.

To my surprise, one of the original engineers turned up at my door.

This time, I lost my patience.

As soon as he crossed the door, I asked if he knew what he was doing this time and if he would finally do his job properly. I pointed out all the issues I’d had since he installed the system and the incompetence I had dealt with. He assured me that this time, he would do everything possible to fix the external piping issues and that he now had much more experience, having installed hundreds of these systems since then (I feel sorry for these people).

External Piping Overhaul

The external piping was completely stripped and reinstalled from scratch.

The flexi hose was corrected and positioned horizontally as it should have been from the start. New valves were installed, along with—surprise, surprise—PrimaryPro insulation.

If I were being picky, I’d say they once again used longer flexi hoses than necessary.

This was even pointed out by the engineers themselves, but they explained that it was what they had been given when they arrived. They ended up unnecessarily extending the pipework along the wall to accommodate the flexi hoses and minimise the bend radius.

(I have since removed the bad review as promised.)

Would I Choose an ASHP Again, Knowing What I Know Now?

Yes, yes, and absolutely yes!

I love how the system works.

Although it's far from being perfectly efficient, currently hovering around a SCOP of 3.2 (5.4 promised on the report), I’m actively working on improving it. I'm still seeking advice on how to make it even better. We don’t have underfloor heating—just radiators—but I know there’s potential to make the system more efficient; I just need some help pinpointing the issues.

I really like how the system performs in winter, with almost no user input required. The heat is distributed evenly throughout the house, without the hot spots we used to have with gas heating.

So yes, I would definitely choose it again. I’d just spend more time doing my homework and finding a better installer.

Final Thoughts

I know this was a long post, but I think the details were important.

All these small issues piled up over months, leading to countless back-and-forths with British Gas over complaints that either took ages to resolve or resulted in me giving up and seeking help elsewhere.

Now, imagine you’re in your 60s, 70s, or even 80s and have to go through this nonsense.

Imagine having to move over 500kg of equipment, including 60kg radiators, from the front of your house, in the rain, to the back to prevent them from being stolen before the installation team arrives. Imagine being shown the SensoComfort controller and told you can only change the temperature up and down like on a gas boiler, without knowing that the system was preconfigured for gas heating with a flow temperature of 60°C, some random high Heat Curve, not weather compensated, which could cost you a fortune if left that way.

I work in the software development industry, and I’m a very thorough person when it comes to research and learning.

I wanted to know everything about this system to get it running at optimal efficiency. I had hoped I would get some help from the people who should have known best—the engineers who installed it—only to find out I had to figure it all out by myself.

Now, try doing all this if you’re in your 60s, 70s, or 80s and can barely use your touch screen phone.

Good luck (no offence of course to older people, but that’s just the reality).

Thanks for reading.