fan hunt on glowworm 120ff

[Dave178]

The boiler works fine if either CH or HW or both are selected, but if both are switched off on the timer, the fan hunts.
Would I be correct to diagnose that the problem is with the air pressure switch,? The plastic air pipes look clear of debris and are in good order.

 

[Tibbot]

This is the DIY forum, you'll get help if you register and post this in the gas combustion section.

 

[Piers1989]

If you refer to the instructions there is a very useful fault finding guide which should cover this issue.

Piers

 

[doitall]

If both are switched off on the timer, should the fan run albeit badly.