Burping boilers

[DP]

Went to an installation (backboiler), where the boiler function nice and dandy for (gravity) hot water.

When CH is selected, the bottom connection gets hotter than top connection on the boiler. Boiler also starts to knock (like venting). When a tumbler full of water is offered to the vent, the vent sucks and blows into the tumbler every time the boiler burps. The water does not fall or rise in the tumbler- it just oscillates. The vent and feed are clear to the tees to the HW cylinder

Any thoughts? Views most appreciated.

 

[weargas]

pump fitted in the wrong direction?

 

[ChrisR]

Boiler h/e blocked so it boils near the bottom and it's easier for vapour to get out of the return connection than work its way to the top? Seems unlikely doesn't it?
I've got rubbish out of feed pipes by connecting mains water to output from f/e tank, or vent. If you tried that you would be forcing water through the h/e. (speedfit & tap flexies useful for that)

 

[PEDANTICVINDICTIVEMAN]

Gaviscon Advanced

 

[ChrisR]

Put it on your shoulder and smack its bottom. I believe it's customary to make silly noises and jump up and down a bit at the same time.