strange combi problem

[timbalcombe]

turned off stop cock in house, drained out all water from cold taps and cistern.
turned it all back on, and now when cold water is drawn from kitchen tap the combi thinks hot water is being called.
Whats happened?

vailant ecotec pro28

 

[timbalcombe]

ok, problem solved. I turned the washing machine on to use the setting which calls for dhw and it seems to have sorted it out!

was it an airlock?

 

[Gasguru]

Air trapped in the washing machine feed pipework is compressed/decompressed each time you open/close the taps and the resultant water flow operates the boilerm DHW flow switch.

 

[Bamber gaspipe]

Air trapped in the washing machine feed pipework is compressed/decompressed each time you open/close the taps and the resultant water flow operates the boilerm DHW flow switch.

Dead leg.

 

[timbalcombe]

what exactly is a dead leg please?

 

[Gasguru]

Pipe containing air normally as the result of bad plumbing practice especially when combi's are installed and the old pipes to the cylinder/feed tanks are left/capped off and not disconnected. Dead legs contravene water regs (G11.7).

I came across a Puma that would fire up for a second on its own - it was due to the mid terraced property sharing the main with next door and a dead leg present in their neighbours pipework. Everytime the neighbours used their taps the boiler would attempt to fire.

 

[timbalcombe]

but these feeds are no longer on the system, the new pipe work bypasses these old pipes.

 

[kevplumb]

the hot water pipes still are

 

[timbalcombe]

impossible, the pipes run under the floor from new boiler.
The dead legs have no way of affecting the system as it is now.

 

[corgiman]

impossible, the pipes run under the floor from new boiler.
The dead legs have no way of affecting the system as it is now.

why not??

 

[timbalcombe]

I can see no way flow or return, how they could be connected.
They all run down from the loft at the same point and are capped midway.

I understand this against water regs?

Cheers for reply.

 

[corgiman]

dead legs are on the old hot water supply and if they have been capped off the air in can expand when a cold water tap is opened and VIOLA the boiler fires up

I think I have explained it right I am sure the others will pick up on it I have made a mistake

PS why are you asking the same question (and getting the same answers) in Screwfix forum

dont you believe Us

or have you made your mind up as to what it and are going to do the rounds till u find a pro to agree wif you

 

[timbalcombe]

just happened to be on screwfix at the time!
Still don't get the dead leg thing as all the old hot water pipes are capped and seperate from the new pipes.
Perhaps its something else a bit dodgy, once, turning on the washing machine cured the problem.

 

[TicklyT]

You haven't necessarily got any dead legs on your system, but your W/M connection would behave like a dead leg until the machine gets used. When the trapped air has been forced out of it, the system would start behaving normally again as you have observed.

 

[timbalcombe]

cheers dude