Overview
E32 on a Keston C36 combi normally means the boiler has detected a short circuit on the domestic hot water (DHW) temperature sensor. The boiler monitors the DHW thermistor to know the hot water temperature; if the control PCB sees an abnormally low resistance (a short) or a direct electrical connection between sensor wires or to earth, it flags E32 and will lock out the DHW function to prevent incorrect operation. On many Keston fault lists E32 is reported specifically as a DHW sensor short circuit (some documents may list similar numbers for other sensors — for this model treat E32 as DHW sensor related). This is an electrical/sensor fault rather than an immediate gas safety emergency, but it will prevent correct hot water control and can cause the boiler to go into fault mode. Severity is medium: it does not usually create a dangerous situation by itself, but it does require safe handling because fixing it involves working inside the boiler where live electrical parts and gas components are present. Because the repair normally requires access inside the casing and possibly replacement of sensors or wiring, this is a job for a qualified Gas Safe engineer. Homeowners can perform a few basic checks (reset, visual inspection outside the boiler, confirm no recent water ingress) but must not attempt internal electrical or gas work unless they are suitably qualified.
Possible Cause: DHW sensor short circuit – check connections to domestic hot water (DHW) sensor
Troubleshooting Steps
Safety precautions:
- Do not attempt to open the boiler or touch internal components while mains power or gas is connected. Isolate the boiler electrically at the fused spur before touching the case. If you are not competent with gas or electrical systems, stop and call a Gas Safe engineer.
- If the boiler has recently had water leakage or condensation inside the case, do not use the boiler until it has been inspected.
- A single reset may clear a transient error but do not repeatedly reset the boiler if the fault returns; this can mask an underlying fault.
Initial checks a homeowner can do (no internal access):
1. Note the conditions when the fault appeared (after power cut, after servicing, after a leak, during rain, after moving pipes, etc.). That helps the engineer diagnose.
2. Try a single reset: press the boiler Reset key once and wait to see if the fault clears and normal DHW operation returns. If E32 reappears immediately or soon after, the fault is persistent.
3. Check for visible signs of water damage, corrosion or physical damage around any external wiring, the flue, condensate pipe or under the boiler. Moisture or leaks can cause sensor shorts.
4. Check other system indicators: does heating still work? Is water pressure normal? Report these to the engineer.
If you are competent with safe isolation and basic electrical testing (recommended only for people with relevant skills):
1. Isolate the boiler electrical supply at the fused spur and confirm no power to the unit. For safety also turn off the gas supply if you will remove the casing.
2. Remove the front cover only after isolation. Take care to follow the manufacturer’s removal instructions so you do not damage fascia cables.
3. Visually inspect the DHW sensor wiring and connector: look for crushed wires, chafing, pinched connectors, corroded pins, loose push-on connectors, or signs of water ingress at the connector. Many faults are a result of a damaged lead or a wet connector.
4. With the wiring disconnected from the PCB or sensor, use a multimeter (continuity/ohms) to check the sensor cable for a short to earth: measure between each sensor conductor and earth/ground — a short will show very low resistance (near 0 ohms). Also measure between the two sensor wires — a short will be very low resistance compared with normal thermistor behaviour. If you are unsure what the correct resistance should be, you are only trying to identify a direct short (very low or near-zero ohms) or an open circuit (infinite).
5. If the cable shows a short to earth or internal short between conductors, trace the wiring back along its route for damage and replace the damaged wiring. If the short is at the sensor head itself, the sensor will need to be replaced.
6. If the cable and connectors look OK, measure the sensor thermistor resistance at ambient temperature with the sensor disconnected. The thermistor is a negative temperature coefficient device (resistance falls as temperature rises); you should not see a near-zero value. If the sensor reads very low resistance or fluctuates wildly, it is likely failed and should be replaced. (If you do not have the sensor’s expected resistance values, report the meter readings to the engineer.)
7. Inspect the PCB connector for signs of burnt pins, corrosion or bridged connections. If the connector or PCB shows damage, do not attempt to repair the PCB yourself — tag this for a qualified engineer.
If the fault is confirmed (short on sensor wiring or failed sensor):
- Replace the DHW sensor and any damaged wiring or connectors. Only a competent person should fit the replacement sensor and re-route or re-terminate wiring.
- After replacement, reassemble the boiler, restore power and gas, then run the boiler and check for normal DHW operation and that the E32 code does not return.
- If replacing the sensor does not clear E32, the fault could be in the control PCB or wiring to the PCB; further diagnostic testing by a Gas Safe engineer will be required.
When to call a professional and what to tell them:
- Call a Gas Safe registered engineer if you are not fully confident to isolate and test the boiler safely, or if your checks show a persistent E32 after reset, sensor reads incorrectly, wiring is damaged, or the PCB/connector looks damaged.
- When you call, tell them: the exact error code (E32), whether a reset cleared it or not, results of any visual inspection, any signs of water ingress, whether heating is affected, and any multimeter readings if you took them.
- A qualified engineer can safely isolate, perform full electrical diagnostics, replace the DHW thermistor or damaged wiring, and if needed replace or repair the control PCB and re-commission the boiler in accordance with the manufacturer’s instructions.
Important note: Any work involving opening the boiler casing, replacing sensors, or working on gas valves and the control PCB should be carried out by a Gas Safe qualified engineer. Attempting internal repairs without appropriate qualifications risks gas leaks, electric shock, damage to the appliance and will likely invalidate any warranty or service agreements.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Keston C36 Combi Gas Boiler.