Vent pipe pumps over when CH turns off

[Agile]

"Most unusual" ?

I recon I see at least one every year and I dont go to that many non combi systems.

Many are probably never diagnosed as wrong.

Whats very sad is that I dont remember ever being asked to correct the problem because of the cost involved.

Tony

 

[Alfie25]

Sorry, i think I may have been confusing matters as I'm still trying to figure ths all out. I have one vent pipe and its over the cold water tank. It comes from the back of the cylinder but also tees off downwards so im not sure if it's linked to the CH system. I would guess not and that I have a combined feed/vent off the CH system. I'll maybe post some pics and do more investigation.

 

[doitall]

How many cold tanks do you have.

 

[ianmcd]

Dear Agile I can assure you I am no DIYr and of course if water is lost via pumping over it will be replaced by the FE tank or the system would run dry, Alfie your boiler requires the pump to be wired directly from the boiler as the boiler has a pump over run facility which will continue running the pump when the boiler switches off if this is required, as you are saying the pump stops immediately I would check how it is wired in good luck Ian

 

[Alfie25]

Dear Agile I can assure you I am no DIYr and of course if water is lost via pumping over it will be replaced by the FE tank or the system would run dry, Alfie your boiler requires the pump to be wired directly from the boiler as the boiler has a pump over run facility which will continue running the pump when the boiler switches off if this is required, as you are saying the pump stops immediately I would check how it is wired in good luck Ian

When the boiler shuts off (burner light goes out) the pump continues running for about 5 minutes. It's when the pump shuts off that I can hear the whoosh/splash of water. I've been up in the loft and not yet observed the water coming out of the vent - I've looked when the pump shuts off after the HW has turned off and again when the CH shuts off. The thing is... once or twice a day the boiler and pump start up for no reason at all (everything is set to 'off' on the programmer) and they run for maybe 2 minutes. It is when this cycle shuts off that I hear the whoosh/splash of water in the loft. Unfortunately I have no idea what time of the day it's going to come on by itself (it varies) and as it only lasts 2 minutes I'm going to have to be quick to get up in the loft and check where this splash is coming from.

As for why it comes on for 2 minutes by iteslf, I have no idea.