BoilerFaultCodesGlow-worm S.53 Fault Code
Also written as S53 — same fault.
The Glow-worm S.53 fault code means: your boiler has temporarily paused because the water temperature is rising too quickly or unevenly, suggesting a circulation issue or a sensor fault.. It appears on 30 Glow-worm models in our database.
Technical description: waiting time: temperature difference flow - return sensor too high (Check thermistor fit)
What causes the Glow-worm S.53 fault?
This fault occurs when the boiler detects that water is heating up far too quickly or that there is a significant temperature gap between the heat going out and coming back. It is physically caused by poor water flow through the unit, often due to a blockage, a failing pump, or a sensor that is no longer reading the temperature accurately. Essentially, the heat cannot be moved away from the burner fast enough, so the system pauses to prevent overheating.
This issue is more frequent in autumn when heating is first turned on after summer, as pump components can seize or sludge can settle during periods of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 bar on the displayBleed all radiators to remove trapped air that might be blocking water flow
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like S.53: no call-out fees, no surprise bills.
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Glow-worm models that show the S.53 fault code
Click a model for the full fault code list and model-specific repair notes.
- 30cxi Repair: £120-250
- 38cxi Repair: £120-250
- Betacom4 Repair: £90-180
- Easicom 24 Repair: £90-180
- Easicom3 Combi Repair: £80-150
- Easicom3 System Repair: £80-180
- Energy Repair: £120-250
- Energy Regular Repair: £90-180
- Energy System Repair: £120-250
- Energy7 Combi Repair: £90-180
- Energy7 Regular Repair: £90-180
- Energy7 System Repair: £90-180
- Essential Repair: £90-180
- Flexicom 18sx Repair: £100-250
- Flexicom 24c / 28c Repair: £90-180
- Flexicom cx Repair: £100-250
- Flexicom hx Repair: £100-250
- Flexicom sx Repair: £100-250
- Sustain 12s Repair: £100-250
- Ultimate 3 25R Repair: £120-250
- Ultimate3 Combi Repair: £90-250
- Ultimate3 System Repair: £100-250
- Ultracom 2 CXI Repair: £90-180
- Ultracom 2 HXI Repair: £90-180
- Ultracom 2 SXI Repair: £100-250
- Ultracom 24cx 30cx Repair: £90-180
- Ultracom 35 Store Repair: £90-180
- Ultracom cxi Repair: £90-180
- Ultracom hxi Repair: £120-250
- Ultracom sxi Repair: £100-250
Source
Glow-worm S.53 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026