Grant E5 Fault Code: Causes, Fixes & Repair Costs
What does the Grant E5 fault code mean?
E5 on a Grant Aerona³ heat pump reports a return water temperature sensor error: the thermistor measuring the water coming back from your radiators or underfloor circuit has failed or is reading implausibly. Together with the flow sensor (code E4), the return reading gives the controller the temperature difference across your heating system — its measure of how much heat the house is actually absorbing — and it feeds frost protection and heat-metering logic besides. Grant's documented remedy is the familiar sensor routine: if the sensor is faulty, it should be replaced, with a resistance check against the table making the diagnosis certain before parts are fitted.
General guidance only — not a substitute for professional advice, and not certified by an heat pump engineer. Always have your specific appliance assessed by a qualified professional. Any heat pump work must be carried out by an MCS-certified heat pump engineer. If you notice a refrigerant leak, a burning smell or water leaking from the unit, switch it off at the isolator and call an MCS-certified heat pump engineer. Refrigerant work must be carried out by an F-Gas registered engineer.
Common causes
- Failed return water thermistor Common
Age and thermal cycling take the element open, short or drifted — the documented cause, settled by a resistance check.
- Wiring or connector fault Sometimes
A chafed lead or corroded connector reproduces sensor failure; the loom is proven before the sensor is condemned.
- Sensor unseated from its pocket Sometimes
A dislodged probe reads its surroundings rather than the water — plausible but wrong values that confuse the flow/return comparison.
How to fix it
- Power-cycle once at the external isolator DIY safe
Switch the heat pump off at its external rotary isolator, wait about three minutes for the inverter capacitors to discharge, and switch back on. One controlled restart is legitimate; if the code returns, leave it for an engineer.
- Have a suitably qualified heat pump engineer complete the documented checks heat pump engineer
The engineer will measure the return sensor's resistance against the table, inspect wiring and seating, replace the faulty sensor, and confirm the flow/return temperature difference reads sensibly through a heating cycle. Work on the sealed refrigerant circuit legally requires an F-Gas registered engineer; your installer or a Grant-accredited (G1) installer is the right call, and Grant UK technical support (01380 736920) can assist with diagnosis.
Parts you may need
- Return water temperature sensor (thermistor) · from £30
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £100–£280, depending on the underlying cause.
Frequently asked questions
What does E5 mean on my Grant Aerona³?
The sensor measuring water returning from your heating circuit has failed. Paired with the flow sensor it tells the heat pump how much heat your home is absorbing, so the unit stops rather than run on half the picture. A confirmed-and-replaced sensor fixes it — an inexpensive repair.
Is this the same fault as E4?
Same class, different probe: E4 is the outgoing (flow) sensor, E5 the return. Diagnosis and cost are essentially identical; the code simply directs the engineer to the right one.
Can I run the heating some other way meanwhile?
If your system includes backup — an immersion heater on the cylinder, or a hybrid setup with a boiler — use that for the interim. The heat pump itself will stay off until the sensor is replaced, which is the correct protective behaviour.