BoilerFaultCodesGlow-worm S.98 Fault Code
Also written as S98 — same fault.
The Glow-worm S.98 fault code means: your boiler is temporarily pausing to check its temperature sensors before heating your home, which may cause a delay in getting hot water or heating.. It appears on 31 Glow-worm models in our database.
Technical description: Flow / Return - sensor check is running, demand (DHW or heating) is blocked
What causes the Glow-worm S.98 fault?
This fault occurs when the boiler detects an unusual difference in readings between its two temperature sensors, prompting it to pulse the pump and compare the figures. The most common reason is that the sensors have become uncalibrated or the water isn't moving through the heat exchanger quickly enough for the boiler to trust the data. If the readings don't align during this check, the boiler will temporarily prevent itself from firing to avoid overheating.
DIY fix possible
Check that all radiator valves are fully openEnsure the system pressure is between 1.0 and 1.5 barWait up to 15 minutes to see if the code clears automatically
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.98: no call-out fees, no surprise bills.
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Glow-worm models that show the S.98 fault code
Click a model for the full fault code list and model-specific repair notes.
- 30cxi
- 38cxi
- Betacom2 28
- Betacom4 Repair: £90-180
- Easicom 24 Repair: £120-200
- Easicom3 Combi Repair: £120-220
- Easicom3 System Repair: £120-250
- Energy Repair: £120-250
- Energy 35 Store
- Energy Regular Repair: £120-220
- Energy System Repair: £120-250
- Energy2 30c
- Energy7 Combi Repair: £120-250
- Energy7 Regular Repair: £120-200
- Energy7 System Repair: £120-250
- Essential
- Flexicom 18sx Repair: £120-220
- Flexicom 24c / 28c Repair: £100-200
- Flexicom cx Repair: £90-180
- Flexicom hx Repair: £120-220
- Flexicom sx Repair: £120-220
- Sustain 12s Repair: £120-250
- Ultimate 3 25R Repair: £120-220
- Ultimate3 Combi Repair: £120-250
- Ultimate3 System Repair: £100-250
- Ultracom 2 CXI Repair: £90-180
- Ultracom 2 SXI Repair: £90-180
- Ultracom 24cx 30cx Repair: £90-180
- Ultracom 35 Store Repair: £90-180
- Ultracom cxi Repair: £90-180
- Ultracom sxi Repair: £90-180
Source
Glow-worm S.98 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
- Glow-worm Ultracom 2 CXI manual (PDF)
- Glow-worm Betacom2 28 manual (PDF)
- Glow-worm Betacom4 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026