Baxi back boiler 50/*

[DP]

Here is another to mull over

Boiler set to stat setting 2. Boiler stat has been replaced.

When boiler starts from cold, every so often it makes a sound like it is venting into the header tank but no water issues from the vent pipe. Placing thumb on the vent indicates slight suction when boiler 'burps'. Air drawn is pressure equalisation instead of air ingress into the system i.e. air drawn is expelled at the end of the 'burp'

HW is Gravity

 

[ArtfulBodger]

That sounds like unequal pressure between the cold feed and the open vent. Has the system been drained & filled recently and was it normal?

 

[PEDANTICVINDICTIVEMAN]

I had a problem with a back boiler because the flow and returns were crossed from new, this caused weird problems as it worked ok most of the time but then periodically it did a similar thing, always allright when I went to look at it, as usual , eventually spotted the crossed pipes and sorted it.