Vent pipe spurting every 5 mins when heating and hw on

[jamescarter1000]

well about 12 years to be precise-they just were not working properley. the new one is red grundfoss.

maybe the system is sludged up. some rads take ages to heat up (although they were balanced recently by a local plumber and are a bit better now, who said theyd been installed (add ons) from another radiators tails!

 

[namsag]

You have described classic boiler stat gone symptons .

Initially takes half hour for water to get far too hot starts turning to steam and expanding thumps bangs on its way up and out the open vent. as hot water is ejected cooler water from header tank enters system cooling it down till it starts overheating minutes later again.

Happens quicker on HW because there is less water to get rid off the heat , ie the rads give off additional heat(surface area etc) to a point but even then it gets to a point where the whole system overheats

 

[granty1]

feel flow and return pipe on boiler, if flow and return is red hot then u know its the stat, if the flow is red hot and the return is cool then it would be sludge or pump.

 

[jamescarter1000]

Thanks for your help - i have to get this sorted this weekend it is doing my head in!!

A final few points though: if the boiler stat failed (as namsag stated and it sounds likely) - wouldn't the room or cylinder thermostat cut out the supply before the boiler stat setting though)? would turning the boiler thermostat down do anything to help it?


Granty1: how would sludge make the flow pipe red hot and the return cooler? please explain as i am confused ... although i believe sludge could be a cause of the pumping over. And the pump is working OK, have had 2 new pumps in past 10-12 years. it sounds ok.

 

[granty1]

if sludge or pump then would cause poor circulation to where the water will be pumped up vent,