Error E37

Safety precautions:

1) If you smell gas or suspect a gas leak, leave the property immediately and call the emergency gas number. Do not attempt internal repairs.

2) Before doing any work on the boiler isolate electrical supply at the fused spur or consumer unit and isolate gas if you will expose gas-carrying components. Only proceed if you are confident and competent; otherwise call a Gas Safe engineer.

3) Allow the boiler to cool before removing covers. Be aware of hot surfaces and hot water in the system.

Initial homeowner checks (safe, simple steps):

1) Reset the boiler using the reset button or power-cycle it at the mains and watch whether the E37 returns. Note if the fault is intermittent.

2) Check the system pressure on the boiler gauge. Low pressure can cause other faults; top up if needed (follow your manual). If pressure repeatedly drops, that indicates a leak which must be investigated.

3) Visually inspect around the boiler and pipework for signs of water leaks, corrosion or condensation, especially at the return pipe and where wiring or connectors are near pipework.

4) Check any accessible external wiring and connectors (e.g. to an external thermostat or programmer) for obvious disconnections or damage.

If you are mechanically and electrically competent and choose to proceed (only if comfortable):

1) Isolate mains power to the boiler and turn off gas supply if you will remove the case. Take photographs of wiring before disconnecting anything so you can restore connections correctly.

2) Remove the front outer case (following the boiler manual’s instructions).

3) Locate the return thermistor on the return pipe and the two push-on connectors on the connector block. Inspect the wires and connectors for corrosion, water ingress, or broken/crimped wires.

4) With the appliance isolated, gently pull off the push-on connectors and inspect the pins and sockets. If connectors are wet or corroded, dry and clean them or replace the connector if damaged.

5) Check continuity of the thermistor wiring with a multimeter: measure resistance between the two thermistor wires. If the meter shows infinite resistance (open circuit) the thermistor is faulty or the wiring is broken. If near zero (short) that indicates a short circuit. If you see a reasonable resistance that changes when you warm the sensor slightly (using a warm cloth or warm water on the pipe) the sensor is likely OK.

6) If the thermistor is faulty or wiring is damaged, unclip the thermistor from its clip on the pipe and remove it. Note: the manual recommends applying a thin smear of heat-sink compound when refitting a new thermistor to improve contact.

7) Fit a replacement thermistor identical to the original (part number from manual or supply), push connectors back in the correct positions, clip the sensor firmly to the pipe, reassemble the casing, restore power, and test the boiler. Re-pressurise the system if you drained any water during work.

When to call a professional (must-read):

1) If you are not confident working inside the boiler, do not remove covers or touch wiring—call a Gas Safe registered engineer.

2) Call a professional if the fault persists after basic checks and a reset, if you find a leak, if wiring or the control PCB appears damaged, or if the thermistor replacement is needed. Any work that involves gas components, significant internal repairs, or commissioning should be carried out by a qualified engineer.

Notes and cautions:

1) Do not bypass sensors or controls to force the boiler to run. That creates unsafe conditions and could cause further damage.

2) The boiler manual includes step-by-step guidance for thermistor replacement; follow manufacturer instructions for isolating the appliance and reassembly. If you replace the sensor, use the correct replacement part and ensure good thermal contact to the pipe.

3) If you are unsure at any point, stop and arrange a Gas Safe engineer visit. Persistent or repeated faults should always be investigated professionally.