Heat Pump Error Codes — What They Mean and What to Do
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →Do not attempt to reset a heat pump fault repeatedly without understanding the cause — some faults indicate safety issues. Do not touch refrigerant pipework.
Heat pump error codes can be worrying — especially when your heating suddenly stops working. Unlike traditional gas boilers, heat pumps are complex systems with refrigerant circuits, electrical controls, and water circulation loops, so when something goes wrong, the fault code is your heat pump's way of asking for help. Most codes are nothing to panic about, but some do require professional attention. This guide walks you through the most common error codes, what they mean, and whether you can safely troubleshoot it yourself or need to call in a qualified engineer. Understanding these faults now means you'll know exactly what to do when the display flashes a code — and crucially, when to stop and reach for the phone.
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Most likely cause & what to check
Heat pumps use error codes to communicate faults — unlike gas boilers, many heat pump faults cannot be safely reset by the homeowner because they may involve refrigerant, electrical systems, or low water flow conditions that need professional assessment.
First step: note the exact code shown on the display or controller app, then look it up in the manual (usually downloadable from the manufacturer's website). Common codes include: flow errors (indicating low or no water circulation), pressure faults, refrigerant-related codes, and communication errors between indoor and outdoor units.
Water flow errors (e.g. Mitsubishi P1, Daikin flow error): these indicate the heat pump cannot detect adequate water circulating through the system. Check that all isolation valves on the heat pump's pipework are open, the system has correct water pressure (usually 1–2.5 bar), and the circulation pump is running. Air in the system can also cause flow errors — bleed radiators and check the expansion vessel.
High pressure or low pressure refrigerant codes: these involve the refrigerant circuit and must be investigated by an F-Gas certified engineer. Do not reset these faults repeatedly — they indicate a potentially serious problem with the refrigerant charge or circuit.
Communication error codes (e.g. Mitsubishi U7, Daikin communication fault): these usually indicate a wiring fault between the indoor and outdoor units, or a controller failure. Power-cycling the system (turn off at the isolator, wait 5 minutes, turn back on) can sometimes clear a transient communication error.
If in doubt, call your heat pump installer or the manufacturer's helpline. Most heat pump manufacturers provide technical support: Mitsubishi Electric 0161 282 3400, Daikin UK 0845 641 9000, Vaillant 0330 100 3461, Worcester Bosch 0330 123 9339, Samsung HVAC 0333 000 0800.
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Frequently asked questions
Can I reset a heat pump fault code myself?
Some transient faults (like communication errors) can be cleared by power-cycling the system — switching it off at the isolator, waiting 5 minutes, and switching back on. However, never repeatedly reset flow errors, pressure faults, or refrigerant codes without understanding the root cause, as these often indicate safety issues that only a qualified engineer should tackle.
What does a water flow error mean and is it safe to ignore?
A flow error means your heat pump isn't detecting adequate water circulating through the system — this could be an open isolation valve, low system pressure, air in the pipes, or a failed circulation pump. It's not safe to ignore because the system won't heat effectively and continued running could damage the heat pump; check the simple fixes first, then call your installer if the error persists.
Do I need an F-Gas certificate to work on a heat pump fault?
Yes — any work involving the refrigerant circuit must be carried out by an F-Gas certified engineer. As a homeowner, you should never touch refrigerant pipework or attempt to diagnose high and low pressure faults yourself, even if the fix seems straightforward.
How often should I check my heat pump for faults?
Heat pumps are designed to run reliably with minimal homeowner intervention, but it's sensible to check system pressure (1–2.5 bar is normal) and listen for any unusual noises during the heating season. Most faults announce themselves with an error code, so you don't need to do regular diagnostic checks — just respond promptly when a code appears.