Medium
F84 on Glow-worm Ultracom 2 18sxi

Your boiler has detected an unusual and lasting temperature difference between the water leaving it and the water returning to it, so it has safely shut down to prevent damage.

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

Permanent temperature difference between flow and return heating sensors

From this model's manual
Verified against the Glow Worm/Glow Worm Ultracom2 12sxi 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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Related fault codes

F75View →F22View →

All 35 fault codes on the Ultracom 2 18sxi

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

ErrF00F01F10F11F20F22F23F24F26F27F28F29F32F49F61F62F63F64F65F67F68F70F71F72F73F74F76F77F83F85F86S.96S.98

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