We had a heat pump installed. Most of what we read beforehand made it sound like a boiler swap with extra steps. It wasn’t. Nothing went catastrophically wrong. But there were a handful of moments where we thought “why did nobody mention this.” So here’s the honest version — the stuff that happened, not the stuff that’s supposed to happen.
If you’re partway through your own install and something on this page sounds familiar, that’s exactly why we wrote it.
The sizing problem nobody warns you about
Before any of the physical work started, there was a sizing headache. Our house needed roughly 8kW of heating output — a completely normal number for a house our size.
The problem: one of the big manufacturers we looked at (Vaillant) jumps straight from a 7kW unit to a 10kW unit. There’s no 8kW option. So the actual choice on the table was:
Undersize to 7kW — slightly short of what the house needs, meaning it has to work harder on the coldest days
Oversize to 10kW — more than the house needs, which usually means it cycles on and off more than an efficient heat pump should, and costs more upfront
Neither is really “right.” It’s just a gap in that manufacturer’s range that happens to land exactly where a lot of ordinary houses sit. We ended up looking at Octopus’s own unit (the Cosy) instead. Partly because its output steps didn’t leave the same awkward gap for our house size.
The lesson, if there is one: ask your installer directly what the output steps are for any brand they’re quoting, and where your house’s number falls. Nobody tells you about the gaps until you’re the one stuck in one.
Two leaks, for two completely different reasons
We won’t pretend the install was leak-free, because it wasn’t — though neither leak was really about the heat pump itself.
Leak one: our system was originally non-pressurised. Switching it over to a pressurised system for the heat pump revealed a weak point that the old, low-pressure setup had never stressed. It leaked. This is apparently a known risk when converting an older system. The pipework’s been sitting quietly under low pressure for years, sometimes decades. Suddenly being asked to hold more pressure finds whatever weakness was already there.
Leak two: after the first leak was fixed, a second one turned up. The engineer had forgotten to replace a radiator valve while dealing with the first issue. Straightforward human error, sorted quickly. But it’s a good reminder that a multi-day install has a lot of moving parts — worth actually checking things over rather than assuming it’s all been done.
Neither leak was expensive or dramatic in the end. Both were mildly stressful in the moment, mostly because nobody had warned us they were even a possibility.
The pipework almost caused a much bigger job
Our house has 10mm microbore pipework — thin pipes, common in a lot of homes from a certain era. Heat pumps generally need slightly wider pipework to move enough water around efficiently, so this is a genuine checkpoint in any survey.
Ours passed — but only just. If the pipework had been marginally narrower, or the layout slightly less favourable, it would have meant a full pipework replacement. That’s a much bigger, messier, and more expensive job than the heat pump install itself.
If you’re getting a survey done: ask specifically where your pipework sits relative to that threshold, not just whether it’s a “pass.” Ours was a pass with very little room to spare, and that’s a very different situation to comfortably clearing it.
The cost nobody mentioned until it was our problem
Our old system ran on LPG, not mains gas. When it’s mains gas being removed, decommissioning it is usually just folded into the installer’s job. LPG is different. We had to separately find and pay for an approved engineer to disconnect the LPG connection before the heat pump install could go ahead.
It wasn’t a huge cost, but it also wasn’t mentioned anywhere until we asked directly why our quote didn’t seem to account for it. If you’re on LPG or oil rather than mains gas, this is worth raising with your installer early, not assuming it’s included.
The LPG tank that wouldn’t leave
We didn’t sign an agreement with AvantiGas, so we weren’t charged for the tank collection. That was the good news.
The AvantiGas letter arrived when we bought the house, before we’d moved in. It said our underground tank was due for replacement. It offered three options: a new tank above ground, a new tank underground, or LPG cylinders. All three kept us on LPG. That’s not surprising from a gas supplier. But it’s one company’s view of your options, not the full picture. The letter pushed us towards a heat pump. So we took none of the options. We needed the tank gone, not replaced.
We moved in during October 2025. The heat pump went in that December. I waited until after the install to chase the tank, then started in January. AvantiGas wouldn’t commit to collecting it within 12 months. I chased by phone and email, many times. They sent someone to resurvey the tank and confirm how they’d remove it. Then I waited again for them to confirm they could fit the job in. Collection only happened because I kept pressing.
We had to arrange the excavation ourselves. Our builders charged £750 to dig the tank out to the requirements AvantiGas set, in June 2026. That was our cost. AvantiGas did not pay it. It will vary with tank size, access and ground.
Once it was booked, removal took about 3 to 4 hours. A tanker came to pump out the remaining gas. Our builders excavated. Then a lorry-mounted crane (a Hiab) lifted the tank away.
AvantiGas never confirmed beforehand that we’d get a refund for the gas left in the tank. When I phoned after the removal, they confirmed one. It was paid by bank transfer about 2 to 3 weeks after collection. I got nothing official showing the volume or the rate per litre. The gas came with the house, so I had no way to know if it was good value.
The lesson, if there is one: get the collection date and the gas refund in writing before anyone digs. This is what happened to us. Your supplier, contract and tank may be completely different.
The room nobody planned for
Our heat-loss survey covered every habitable room in the house — bedrooms, living spaces, the works. Our en-suite wasn’t one of them. It’s classed as non-habitable, so it fell outside the calculation entirely. Nobody flagged it, because on paper there was nothing to flag.
What the paperwork didn’t account for: it’s a small room with three external walls. Once the heat pump was running, it was the one room in the house that stayed stubbornly cold.
We didn’t discover this until we’d been living with the system for a while — it’s the kind of thing you only really notice once you’re through a full heating season. Once we did, we pushed our installer to fix it. To their credit, they took on the cost. But because we wanted a specific designer radiator to fit the space and match the room’s look, we ended up working within a real ceiling on how much output we could physically fit in — smaller, stylish radiators simply don’t have the surface area to output as much heat as a plain panel radiator of the same size. We landed close to what the room needs, not comfortably above it. It’s fine day to day, but there isn’t much headroom if a cold snap pushes it.
The lesson isn’t “get a boring radiator.” It’s this: “non-habitable” is a planning category, not a guarantee the room won’t get cold. If a room like this has multiple external walls, ask specifically whether it’s been included in the heat-loss numbers — not just assumed fine because it’s small.
The kitchen with nowhere for a radiator
Our kitchen didn’t get a new radiator during the switch. It couldn’t — there wasn’t a single stretch of wall left to put one on. Units, worktops and appliances had already claimed every usable space.
This isn’t a heat pump problem specifically — it’s a kitchen problem that heat pumps just make you confront properly, because a heat pump can’t paper over a room with nowhere for a radiator the way a boiler running hotter water sometimes can.
Our kitchen and dining room are open to each other, so instead of forcing a radiator into a kitchen that had no room for one, we sized up the dining room’s radiator to heat both spaces together. That’s a big part of why our dining room’s radiator ended up so much larger than before — it’s not just heating the dining room, it’s covering the kitchen’s share too. It works, but it only works because the opening between the two rooms is wide — warm air needs somewhere to actually flow if one radiator’s doing the job of two rooms. If your kitchen and the room next to it are only connected by a narrow doorway, this approach won’t carry the same way.
If you’re planning a heat pump switch and your kitchen has no wall space free, it’s worth raising with your installer early rather than assuming it’ll sort itself out at survey stage. The options tend to be: a slimline radiator in whatever gap exists, an electric panel heater on its own circuit, underfloor heating if you’re already pulling the kitchen apart, or sharing an oversized radiator with an adjoining room the way we did.
Would we do it again?
Yes, honestly. None of this was a reason to regret it — it’s a reasonably involved job, and involved jobs have snags. What would have made the whole thing smoother wasn’t a different heat pump. It was simply knowing these four things existed as possibilities before we started, instead of discovering each one as it happened.
That’s really the only reason this page exists.
A couple of honest disclosures
We use Octopus Energy ourselves, both for our tariff and for the heat pump install. We have referral codes for both — using them can get you a discount, and gets us a small thank-you too. We’re not going to pretend that’s not the case.
Who this doesn’t suit: if you’re not already looking at Octopus as an option, or a different supplier or installer clearly makes more sense for your situation, don’t force it just because of a code below. The rest of this site is built to help you work out what’s actually right for your home. This page is the one place that’s personal rather than neutral — it’s clearly marked as such for exactly that reason.
If you do want to use them:
Energy switch referral code: A split of £100 50:50 with every sign up. £150 if you’re a business.
Heat pump install referral code: see how it works
Just Ask: Heatpump
Just Ask: Heatpump is an independent companion to Visit a Heat Pump and Get a Heat Pump. Built from real installation experience to give honest, practical guidance before you commit. Everything here is about air-to-water air source heat pumps.
© 2026 Michael Pope
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