Keston E32 Fault Code: Causes, Fixes & Repair Costs
What does the Keston E32 fault code mean?
The E32 fault code signals that a temperature sensor has reported an electrically invalid reading — specifically a short circuit — to the boiler's control board. Exactly which sensor is involved depends on your Keston model: on the C36 combi, E32 points to the domestic hot water (DHW) sensor; on the C40, C55, C90, and C110, it indicates the return thermistor. In both cases the principle is the same — the PCB is receiving an impossibly low resistance reading from the sensor, which tells it something is seriously wrong, and the boiler shuts down into lockout or block mode as a safety measure. The boiler will not restart until the underlying fault is resolved and the reset button is pressed.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Short-circuited thermistor or DHW sensor Common
Thermistors work by changing their electrical resistance as temperature rises or falls, feeding that data continuously to the PCB. A true short circuit means two conductors have made unintended contact inside or around the sensor, sending the PCB a resistance reading that is impossibly low. The board correctly interprets this as a fault and locks out. On the C36 this is the DHW sensor; on C40 and above it is the return thermistor.
- Damaged or corroded wiring and connector plugs Common
The wiring loom and plug connecting the thermistor to the PCB is exposed to heat cycling over years of use. Connectors can corrode, wires can chafe against pipework, or the plug can work loose — any of these can create a low-resistance path that mimics a short circuit even if the sensor itself is perfectly healthy. Keston specifically advises checking and replacing connections as a first step.
- Water ingress or a nearby leak Sometimes
A small leak close to the thermistor or its wiring can allow water to bridge the sensor terminals or soak the connector, producing a short circuit. This is worth ruling out carefully, since a persistent leak can cause recurring faults and may signal a wider problem such as a corroded heat exchanger or a failing seal.
- Failed thermistor component Sometimes
Even without any visible damage or moisture, thermistors do fail with age. Internal degradation of the component causes it to report erroneous resistance values. When replacement of the wiring and connectors does not resolve E32, the thermistor itself is usually the culprit and will need to be swapped out.
- PCB fault caused or compounded by the short circuit Rare
In rare cases a sustained short circuit can damage the PCB itself, meaning that even after fitting a new thermistor the fault persists. This is an unusual outcome but is more likely if the boiler has been run through repeated lockout-reset cycles with the underlying short still present.
How to fix it
- Check that your gas supply is working DIY safe
Before assuming the boiler has a component fault, confirm that other gas appliances in your home — hob, gas fire — are working normally. If your gas supply is off or interrupted, contact your gas supplier rather than an engineer.
- Note which model you have before calling an engineer DIY safe
E32 means something slightly different depending on your boiler: on the C36 it is the DHW sensor, while on the C40, C55, C90, and C110 it is the return thermistor. Having your model number to hand (usually on a label inside the boiler casing) will help the engineer arrive prepared with the right parts.
- Reset the boiler once DIY safe
Press and hold the reset button for the period specified in your Keston user guide (typically 3–5 seconds). If the boiler fires up and runs normally, monitor it closely. If E32 returns within a short time, do not keep resetting — repeated resets without resolving the underlying fault can mask the problem and, in the case of a water-related short, risk further damage.
- Have a Gas Safe engineer inspect the thermistor wiring and connector Gas Safe engineer
The engineer will isolate the boiler and carefully examine the wiring harness and connector plug leading to the DHW sensor (C36) or return thermistor (C40–C110). Corroded pins, chafed insulation, and loose plugs are all common findings and are straightforward to address if caught early.
- Have the engineer check for any water leaks near the sensor Gas Safe engineer
Water ingress is a specific cause called out in Keston's own guidance for this fault. The engineer should inspect the surrounding pipework, seals, and heat exchanger for signs of dripping or moisture tracking toward the sensor area. Any leak found should be repaired before the thermistor is replaced, otherwise the new part may fail quickly.
- Have the thermistor electrically tested and replaced if faulty Gas Safe engineer
Using a multimeter, the engineer will measure the thermistor's resistance at ambient temperature and compare it to the expected value for that sensor. If the reading is outside specification or the sensor is shorted, the component will be replaced. Thermistor parts for Keston boilers typically cost £15–£40; access difficulty varies between models, which affects labour time.
- Ask the engineer to check PCB integrity after replacement Gas Safe engineer
Once a new thermistor is fitted, the engineer should confirm the PCB is reading the sensor correctly and that no secondary fault codes are present. If E32 persists after a confirmed good sensor and clean wiring, the PCB may have been damaged by the original short circuit and will need further investigation.
- Call a Gas Safe registered engineer with Keston experience Gas Safe engineer
Keston boilers use a twin-flue design and a modulating pump arrangement that not all engineers are equally familiar with. When booking, it is worth asking whether the engineer has worked on Keston appliances before. All sensor, wiring, and PCB work on a boiler must be carried out by a Gas Safe registered engineer — this is a legal requirement in the UK.
Parts you may need
- DHW sensor (Keston C36) · from £25
- Return thermistor (Keston C40/C55/C90/C110) · from £30
- Wiring harness/connector loom · from £35
- PCB (if damaged by short circuit) · from £280
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–£250, depending on the underlying cause.
Frequently asked questions
Can I fix a Keston E32 fault myself?
No. Although you can safely reset the boiler once and check your gas supply is on, any work on the thermistor, its wiring, or the PCB must be carried out by a Gas Safe registered engineer. Keston boilers are particularly specialised appliances, and attempting DIY repairs on internal components is both dangerous and likely to invalidate any remaining warranty.
Why does E32 mean different things on different Keston models?
Keston uses the same error code across its range, but the sensor it refers to changes depending on the boiler's design. The C36 combi has a dedicated domestic hot water sensor that can develop a short circuit, while the larger C40, C55, C90, and C110 models flag E32 for a short circuit on the return thermistor instead. The repair approach is very similar in both cases, but the location and part number of the faulty sensor will differ, so always confirm your exact model before ordering parts.
How much does it typically cost to repair a Keston E32 fault in the UK?
Most homeowners pay somewhere between £100 and £250 all-in for a thermistor replacement, covering the engineer's call-out, labour, and the part itself (which is usually £15–£40). If a water leak has also damaged the PCB, costs can rise significantly — a replacement PCB typically adds £180–£400 to the bill. Engineers in London and those working for large national firms tend to charge noticeably more than independent local Gas Safe engineers, so it is worth getting two or three quotes.
My Keston boiler is over 12 years old and showing E32 — should I repair or replace it?
If the fault is limited to a thermistor or its wiring, repair is almost always the more economical choice regardless of age. However, if the engineer also finds a damaged PCB, a water leak from a corroded heat exchanger, or other worn components, the combined repair bill can approach the cost of a new boiler. As a rough guide, if repair costs are likely to exceed around 50% of the price of a suitable replacement, and the boiler is over 12–15 years old, replacement is worth serious consideration — a modern condensing boiler will also be considerably more efficient.