pumping over - sort of

[doitall]

So what happens is when CH switches off it seems that pump stops dead

Don't you need any pump overrun with your boiler???
Maybe if the pump ran on and things cooled a bit the 'pump over' would stop too.

Dont say what boiler, but if installed correctly you need no more than a 1m head.

To pump over the system is out of balance.

 

[Malc]

No the boiler (oil fired, HRM Wallstar) does not need or have any overrun. In any case as it occurs when the pump stops then it wouldn't matter when it stops. I've tested it with the boiler off and it still does this so the boiler temperature is not a factor.

When you say 1m do you mean 1m between top of water in feed tank and the bend in the vent pipe? If so there may not be 1m as the roof has a very low pitch. You have to crawl in the loft space so perhaps 4 foot at the highest and the feed tank is off to one side. Main water tanks are on the centre line. I've taken the pipe up to the roof then back down again and lowered the water level so that's all the head room I have.

 

[doitall]

No by 1m I mean fron the bottom of the tank to the highest part of the system.

 

[Malc]

Towel rad is the highest but that has 1m to the ceiling, then there is the joists and a couple of inches in the header tank, say at least 1.1m.

However, since my problem was the water sloshing up the vent pipe when the pump stopped I don't see the relevance of the head. The feed is next to the vent which is next to the pump inlet. Hence all the CH is at 1.1m or more when the pump is running.

 

[doitall]

Ok