Heat pump hot water problems: noise, winter cold and error codes Usually not a lemon — here's what's really going on.
If your heat pump hot water system is buzzing at 2am, running cold on a frosty morning, or flashing a code, the honest news is that most of these are not a faulty unit. They are far more often an undersized tank, a badly set run-timer, poor placement, a clogged air filter, or a model that was never rated for a cold climate. This guide walks through each symptom, what you can safely check yourself, and the exact point where you should stop and call a licensed installer. If you are still deciding whether to buy one at all, start with is a heat pump hot water system worth it?
Reviewed by the Mission Green Energy Team · Updated July 2026
Is your heat pump broken,
or just badly set up?
The honest short answer before you spend money on a call-out or a replacement.
Most heat pump hot water ‘faults’ are not a defective unit — they are a set-up problem. In one Australian installer’s experience across more than 650 installations, only two households complained about noise, and both were fixed by changing the run-timer or switching on a quiet fan mode — not by replacing anything (source: SolarQuotes).
The four complaints we see most often each have an ordinary cause: noise is usually placement or timing; running out of hot water is usually an undersized tank or a timer set too tight; poor winter performance is usually a unit falling back to its electric element or one never rated for your climate; and an error code is very often just a blocked air filter. Work through those before you assume the worst — and know exactly where the DIY line stops and licensed work begins.
“It’s too loud”
is nearly always a placement fix.
The noise concern is real but overstated — and it is almost never the unit itself.
Here is the honest frame: a well-made heat pump runs quietly. Quiet units sit in the low-40 decibel range and even louder models sit in the low-50s — noticeably quieter than a typical outdoor air-conditioner, which sits in the mid-60s (source: SolarQuotes). If yours seems loud, the problem is usually where and when it runs, not the compressor.
Running at 2am under a bedroom window
A unit set to run in the dead of night, mounted against a bedroom or a neighbour’s wall, is the single most avoidable cause of noise complaints. The fan and compressor are gentle by day and intrusive at 2am simply because everything else is silent.
Re-time it to the daytime
Shift the run window to the middle of the day — something like 8–11am and 3–5pm. That also lets it soak up your own solar instead of grid power, so you cut noise and running cost in one change.
Quiet-fan mode and siting
Many units have a ‘quiet fan’ setting for a small efficiency trade-off. Combine it with sensible placement — open airflow, away from sleeping areas and reflective corners — and the complaint usually disappears without a technician.
Running out of hot water
is usually sizing or timing.
A cold shower at the end of the queue is almost always an undersizing or timer issue, not a fault.
Heat pumps heat a tank more slowly than an instant gas unit, so if the tank is too small for the household or the timer only lets it run in a narrow window, you can empty it faster than it refills. A full reheat takes roughly 3–5 hours, but because hot water stratifies to the top of the tank you rarely need the whole tank hot before you can shower (source: SolarQuotes).
Match the tank to the household
As a guide: around 150 L for 1–2 people, 270–350 L for 4–5 people, and a minimum of about 315 L for 6 or more. The ACT Government’s buyers guide uses a standard storage range of roughly 150–315 L. If yours is at the small end for your family, that is the likely culprit.
Give it room to recover
If you have set a tight run window to chase cheap power or solar, it may not have time to reheat before the evening. Widen the window or add a midday top-up so the tank is full before peak shower time.
New house or new habits
A system that coped last year can fall short after a new occupant, a new baby, or longer showers. The unit has not failed — the demand changed. Re-sizing the timer, or a larger tank at replacement, is the fix.
Cold mornings, weak hot water
and why it is usually the model, not a fault.
Losing efficiency in the cold is normal physics — the question is whether your unit was rated for your climate.
A heat pump pulls warmth from the air, so its efficiency (COP) naturally falls as the air gets colder. Around 10°C ambient many units run at a COP of roughly 3–4; at −5°C that can fall to about 2; and near −10°C it may be 1.5 or lower (source: SolarQuotes). That is not a defect — it is what every heat pump does. The real issue is what your unit does when it gets cold.
Cheaper units — often those using older R134a refrigerant — simply switch to their built-in resistive electric element in cold conditions, which quietly pushes your running cost up. A unit rated for a cold climate instead keeps working on the heat pump itself, down to roughly −10°C at reduced efficiency. Refrigerant type is the tell: R290 (propane) is low-emission but flammable, while R744 (CO2) is engineered to hold up in the cold, though it costs more up front.
It's flashing a code
— start with the filter, then the manual.
The most common trigger is the cheapest to fix, and the code itself is brand-specific.
Before you panic at a fault code, check the air path. A blocked air filter is a common trigger for airflow-related error codes, and a clean-and-reset often clears them. Cleaning the filter and clearing the vents around the unit are simple owner tasks (source: SolarQuotes).
Beyond that, there is no universal code list. Error codes differ by brand — different manufacturers number the same underlying fault completely differently — so the only reliable move is to read the code off the display and look it up in your unit’s own manual, not a generic list online. That tells you whether it is a nuisance airflow trip you can reset or something that needs a technician.
What you can safely touch
and what is licensed work.
Get this line right and you protect both your safety and your warranty.
Filter, airflow, reset
Cleaning the air filter, clearing leaves and clutter from the airflow and vents, and operating the temperature-pressure relief (PTR) valve as a periodic check are ordinary owner tasks. A clean-and-reset clears many nuisance faults on its own.
Refrigerant, wiring, anode, PTR swap
The refrigerant circuit, electrical wiring, replacing the PTR valve, and replacing the sacrificial anode are all licensed plumber or technician work. These are not DIY jobs — getting them wrong is a safety risk and can void your cover.
Keep to the service schedule
Skipping the maintenance the manufacturer specifies can reduce or void the warranty. Keep a simple record of filter cleans and any service visits so a future claim is not knocked back on a technicality.
Before you call it a lemon,
work through this order.
Most problems clear without a replacement — and often without a call-out.
If it is noisy, re-time it to the daytime and try quiet-fan mode before anything else — that fixes the overwhelming majority of noise complaints and cuts your running cost too. If you are running out of hot water, check the tank size against your household and widen the run window; a cold shower at the end of the queue is nearly always sizing or timing, not a fault. If it struggles in winter, find out whether your model is rated to keep running on the heat pump in the cold or is quietly falling back to its electric element — that is a model-choice issue, most relevant if you are in a genuinely cold zone. If it throws a code, clean the filter, reset, and look the code up in your own manual. Only when those are exhausted — or when the manual points to refrigerant, wiring or the board — is it time for a licensed technician. And if you are still deciding whether a heat pump suits you at all, read is a heat pump hot water system worth it? first.
Heat pump hot water problems
your questions, answered.
It is usually placement or timing, not a faulty unit. Well-made heat pumps run quietly: quiet models sit in the low-40 decibel range and even louder ones sit in the low-50s, which is noticeably quieter than a typical outdoor air-conditioner in the mid-60s. The classic cause of a noise complaint is a unit set to run at 2am against a bedroom or neighbour's wall, when everything else is silent. The fix is almost always to re-time it to the daytime, such as 8 to 11am and 3 to 5pm, or switch on a quiet-fan mode, rather than replace anything. A genuine rattle or grind is different and worth logging with your installer under warranty.
This is nearly always an undersizing or timer issue rather than a fault. As a rough guide, a tank around 150 litres suits 1 to 2 people, 270 to 350 litres suits 4 to 5, and 6 or more needs a minimum of about 315 litres. A full reheat takes roughly 3 to 5 hours, but because hot water stratifies to the top of the tank you rarely need the whole tank hot before you can shower. If you have set a tight run window to chase cheap power, it may not have time to recover before evening, so widen the window or add a midday top-up. A system that coped last year can also fall short after a new occupant or longer showers.
Losing efficiency in the cold is normal physics, not a defect. A heat pump draws warmth from the air, so its efficiency (COP) falls as the air cools: around 10 degrees it may run at a COP of 3 to 4, at minus 5 degrees around 2, and near minus 10 degrees 1.5 or lower. The real issue is what your model does when it gets cold. Cheaper units, often those using older R134a refrigerant, switch to their built-in electric element in cold conditions, which pushes running cost up. A unit rated for a cold climate keeps working on the heat pump itself. In cold zones, choose a model rated to run on the heat pump down to about minus 5 degrees with a COP of at least 2.
Start with the air filter. A blocked filter is a common trigger for airflow-related error codes, and a simple clean-and-reset often clears them. Beyond that, there is no universal code list: error codes differ by brand, and different manufacturers number the same underlying fault completely differently. The only reliable step is to read the code off the display and look it up in your own unit's manual, not a generic list online or another brand's chart, because a matching number can mean an unrelated fault. If the manual says the code points to a sensor, refrigerant or electrical fault, treat it as a call-out for a licensed technician rather than something to reset yourself.
Cleaning the air filter and clearing leaves and clutter from the airflow and vents are simple owner tasks, and a clean-and-reset clears many nuisance faults. Operating the temperature-pressure relief (PTR) valve as a periodic check is also an owner task. However, the refrigerant circuit, electrical wiring, replacing the PTR valve, and replacing the sacrificial anode are all licensed plumber or technician work and should never be DIY, both for safety and because unauthorised repairs can void your warranty. Skipping the maintenance the manufacturer specifies can also reduce or void cover, so keep a simple record of your filter cleans and any service visits in case you need to make a claim later.
Work through the easy checks first: re-time a noisy unit and try quiet-fan mode, check tank size and the run window if you are running short of hot water, and clean the filter and reset if a code appears. Call a licensed installer when those are exhausted, when the unit still underperforms after a filter clean, or when your manual says a code points to refrigerant, a sensor, the electrical wiring or the control board. Anything involving the refrigerant circuit, wiring, the PTR valve or the anode is licensed work by law. Where possible, make the call while the system is still under warranty so a genuine fault is repaired at no cost to you.
Where these figures come from.
Every figure above traces to one of these primary sources. Where numbers can vary by model or climate, confirm against your own unit's manual and datasheet.
- SolarQuotes — How noisy are hot water heat pumps really? (decibel levels, placement and run-timer fixes)
- SolarQuotes — Heat Pump Hot Water buying guide (refrigerants, COP vs temperature, tank sizing and reheat time)
- SolarQuotes — Heat pump maintenance (DIY filter and PTR valve vs licensed work, brand-specific error codes, warranty)
- ACT Government — Singing in the shower: a guide to hot water heat pumps (cold-climate rating, booster element, tank size)