Scotland Regional Winner, Heating Installer Awards 2026Highly Commended, Scottish Energy Efficiency Awards 2025
🎉 Scotland Regional Winner at the Heating Installer Awards 2026
Scotland Regional Winner, Heating Installer Awards 2026Highly Commended, Scottish Energy Efficiency Awards 2025
🎉 Scotland Regional Winner at the Heating Installer Awards 2026
Home / Blog / Heat pump troubleshooting
What to check first, in the order that rules things out fastest, before you ring anyone, from the engineer who fits and fixes these systems.
Sean Hogan · Heat Geek engineer · Updated October 2026 · 6 min read
Your heating goes cold and the first thought is always the worst one: has the heat pump actually broken? In the large majority of call-outs we get, it hasn’t. Something’s tripped, a schedule’s changed, or the outdoor unit is working through a normal defrost cycle rather than failing outright. This guide walks through exactly what to check, in the order that rules things out fastest, before you ring anyone.
Short answer: most of the time it isn’t a breakdown. It’s a tripped isolator switch, a paused schedule, or the outdoor unit blocked by snow or leaves. Work through the checks below in order before you call anyone. If you reach the end and it’s still not heating, that’s when you call us.
Start with the power. Look at the isolator switch fitted next to the outdoor unit, then check the fuse or MCB for the heat pump circuit in your consumer unit. A unit that’s tripped the electrics shows a completely blank display, not an error message, and that distinction matters: a blank screen is a power problem, a screen with a code on it is something else entirely.
Next, check the app or control panel hasn’t been left on holiday mode, or that a schedule change didn’t accidentally switch the heating off. This happens more often than an actual fault, especially straight after someone’s been in the app adjusting the hot water timer or setting a weekend away. It takes thirty seconds to check and rules out the single most common cause of a “dead” system before you do anything else.
If the power’s on and the schedule looks normal, look at the outdoor unit itself. Snow banked against the casing, leaves blocking the fan, or a heavy build-up of ice on the coil will all stop it running properly. Clear loose snow and leaves by hand. Don’t chip at ice with anything sharp, that can damage the coil fins and turn a five-minute check into an actual repair.
A heat pump pulls heat out of the outside air, and in cold, damp conditions that means moisture in the air condenses and freezes on the outdoor coil. Every heat pump handles this the same way: it runs a short defrost cycle, several times a day in the worst conditions, where it briefly reverses to melt the ice off before going back to heating. During that cycle the fan can slow or stop, you might hear a change in noise, and the unit can look like it’s doing nothing useful for a few minutes. None of that is a fault.
What throws people is timing. If you check the unit mid-defrost it looks stalled, and it’s tempting to assume the worst. Give it 20 to 30 minutes. If the frost hasn’t cleared and the system’s no closer to heating by then, that’s worth a call. Scotland’s west coast in particular sits in exactly the temperature and humidity band, roughly 0°C to 5°C with high moisture, that triggers the most frequent defrost cycling of anywhere in the UK. More frequent cycling in that band is normal operation here, not a sign your specific unit is struggling. Our guide to how efficient heat pumps actually are in Scottish winters covers the wider picture if you want the detail.
One thing worth checking separately in freezing weather: the condensate drain, the small pipe that carries the unit’s own defrost water away. A blocked or frozen drain is one of the most common winter call-outs, and it’s the unit’s own water freezing back up, not a sign anything inside has actually broken.
Get it checked over the phone before assuming the worst.
“Sean from Aventus was able to face time my dad and talk him through concerns about how his air source heat pump was performing during cold weather . We managed to resolve the issues with Sean’s patient help and expert knowledge.”
Sid Ambrose, ★★★★★ Google Review
A heat pump splits its output between space heating and hot water using a diverter valve, one device switching flow between your radiators or underfloor loops and the cylinder. Because that valve, the cylinder’s own thermostat, and the heating circuit are effectively separate systems sharing one heat source, it’s entirely possible for one to fail while the other keeps working normally.
If the heating’s running fine but the taps have gone cold, the fault is more likely sitting with the diverter valve, the cylinder’s immersion backup, or a hot water schedule that’s been changed in the app, not the heat pump’s compressor.
The reverse pattern, hot water but no heating, points the same way: check the heating schedule and zone controls before assuming a bigger problem.
Either way, this is a case where telling us which one’s affected, heating or hot water, saves real time on the call-out, since it narrows down which part of the system needs looking at first.
We’ve written a full breakdown of what different noises usually mean and when they’re worth worrying about in our guide, are heat pumps noisy, rather than repeating it here. The short version for a system that’s stopping and starting: check the power and outdoor unit steps above first, since a partial electrical fault or a unit struggling against blocked airflow both commonly show up as short-cycling before they show up as anything else.
Most heat pumps sold and installed in Scotland today show a fault code on either the outdoor unit’s own display, an indoor wall controller, or the manufacturer’s app, myVAILLANT, Aquarea Smart Cloud and similar. When one appears, don’t try to interpret it yourself.
What actually helps is noting the code exactly as shown, letters, numbers and any decimal point included, and having it ready when you call. That single piece of information tells an engineer roughly what area of the system to expect trouble in before they’ve even left the van, which usually means a faster, more accurate first visit rather than a guessing exercise on your doorstep.
Send us a photo of the display and we’ll tell you what to expect before booking anyone out.
“Our heat pump had been incorrectly installed by another company that has since gone into liquidation, leaving us with nearly three years of no heating, ongoing faults, and constant leaks. Aventus Eco truly saved the day. Sean quickly identified the issues that had caused continuous problems for years and resolved them properly.”
Alison McLean, ★★★★★ Google Review
Most of what lands on our books as a “broken” heat pump turns out to be one of the checks above. A genuine fault has a different pattern.
In every one of those cases, don’t keep resetting it. Repeated resets can mask the actual fault by the time an engineer arrives, making the eventual diagnosis slower rather than faster. Whether a repair or a full replacement makes more sense at that point usually comes down to the age and condition of the system, which our guide to how long heat pumps actually last covers in more detail.
Get it looked at properly, whoever installed it originally.
“Sean went out of his way to fix a heat pump he hadn’t even installed. I would recommend him highly.”
Louise Allen, ★★★★★ Google Review
When you call with a fault, the first questions are exactly the ones this guide covers:
That’s not box-ticking, it genuinely narrows down what an engineer needs to bring and shortens the visit. Our engineers, the same team installing heat pumps across Glasgow and the central belt, carry diagnostic equipment for every major brand we work with rather than guessing from a call-out sheet.
It’s also worth knowing that manufacturer warranties are conditional, not automatic. Most require a documented annual service to stay valid, and a repeated DIY reset attempt on a genuine fault can complicate a warranty claim if it’s not clear afterwards what actually caused the failure. Keeping up an annual service, covered in full in our guide to heat pump servicing and maintenance in Scotland, is the single most reliable way to avoid repeat call-outs like the one you’re dealing with today, and it protects the warranty that’s meant to cover you if something does go wrong.
Most of the time it’s a tripped isolator switch, a holiday-mode override in the app, or the outdoor unit blocked by snow or leaves rather than a genuine fault. Work through the power, schedule and outdoor-unit checks in this guide before assuming the worst.
Yes. A heat pump runs short defrost cycles in cold, damp conditions to clear frost from the outdoor coil, and the fan can slow or stop briefly during one. Give it 20 to 30 minutes; if nothing’s changed by then, that’s worth a call.
Heating and hot water run through separate controls off the same heat pump, split by a diverter valve. A fault on one side, commonly the diverter valve, the cylinder thermostat or the hot water schedule, can leave the other working normally.
You can turn it off and back on once at the isolator switch next to the outdoor unit. If the same problem comes straight back, stop there rather than repeating the reset, and call us instead, since repeated resets can make the actual cause harder to diagnose.
It varies by manufacturer, and codes change between firmware versions, so don’t try to interpret it yourself. Note the code exactly as shown and have it ready when you call; it tells an engineer roughly what to expect before they arrive.
Most manufacturer warranties require a documented annual service to stay valid, and refrigerant-circuit work on most systems is legally restricted to F-Gas certified engineers. The checks in this guide, power, schedule and clearing the outdoor unit, are all safe to do yourself; anything beyond that should go to an engineer.
The fastest way to get clarity is to talk it through with someone who can actually see what the system is doing, not guess from a call-out sheet.
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