Medium
Cylinder Thermistor Fault on Keston Heat 55

Your boiler is struggling to read the temperature of your hot water cylinder, which usually means it cannot properly tell when your water needs to be heated.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Check Cylinder Thermistor Wiring, Check Cylinder Thmr (10K @ 25°C, 2K at 66°C)

From this model's manual
Verified against the Keston/Keston Heat 45 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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All 36 fault codes on the Heat 55

Seeing a different code? Every code this model can display, in one place.

167475767778798081828384858687888990BCC FaultError 20Ext’ Interlock OffFalse Flame LockoutFan FaultFlame LossFlow/Flue Thermistor FaultFlow/Return ReversedFlue Thermistor FaultIgnition LockoutLow Mains VoltageLow Water PressureOutside Sensor FaultOverheat LockoutPCB FaultReturn Thmr FaultToo Many Resets

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