Low Information
S.98 on Glow-worm Ultracom 35 Store

Your boiler is temporarily pausing because it has detected a suspicious temperature difference and is double-checking that its heat sensors are working correctly before it continues.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Flow / Return - sensor check is running, demand (DHW or heating) is blocked

What causes this fault?

This fault occurs when the boiler's internal computer notices the temperatures on the two main pipes don't match up as expected. To prevent overheating, the system pauses briefly to test if the sensors are providing accurate data or if they are beginning to fail. The most common reason is one of the sensors becoming slightly out of calibration, causing a 'clash' in the readings.

Engineer required

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

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