New Vaillant combi. Any cold mains tap or valve is closed boiler seems to sense increase in pressure and turns itself on. I imagine without investigating further that it is heating the small hot water store as it does do intermittently anyway. This happens every time so it isn't coincidence. Any ideas?
Hi Mike,
Massive coincidence... I was just searching the forum as I have this issue and your post appeared!! I am getting similar symptoms on my newly installed Glow-Worm combi. I have an engineer visiting tomorrow about a separate issue (loud rumbling) but I will ask him about this as well. Watch this space!
J
Possibly a deadleg of hot water pipework somewhere which is full of air. The pressure increase in the cold supply as you turn off a tap due to the momentum of the incoming water will result in the air deadleg being compressed by water momentarily flowing through the boiler. I don't know how the hot water store works in that boiler, but maybe the air could be trapped in there?
In addition to AG's reply which I believe to be correct. You can switch your boiler from intermittently heating the HW by turning the HW knob fully anticlock and then back to where it was. This will save gas but the HW will take longer to come through hot.
I have a deadleg as a temporary measure when swapping over from the stored water conventional system to this one. As I have good ceiling and floor I have capped off the hot supply from the old cylinder, so maybe it is there. I'll try flexing the capped end down and whilst SWMBO runs the taps bottom to top. The boiler itself has a bleed program that does heating and hot water. I've run this twice, so I'd expect internal components to be properly bled. Shag, I've just thought - haven't bled the washing machine...
Thanks AG!
The bleed program is for the primary side of the boiler. There is not much pipework for any significant amount of air to get stick in the domestic side.
My parents WB combi (there is no HW storage in this one AFAIK but I would have to check) also fires up when certain cold taps are used. This is only caused when the outside tap or utility room cold taps are used and these are the only taps between the combi and the main stop tap. No other taps cause this "problem"
Is there any chance that these taps are causing a pressure drop that makes the combi think HW has been called for?
Adam
I still think you need some sort of dead leg (or maybe very poorly clipped pipework) after the boiler on the HW pipes to get this effect.
I still have the problem I looked up dead leg to ensure I understood you, could you clarify please Ed?
I have tried all I can think of, and with knowledge of all my pipework, to eradicate any air.
As I mentioned I do have a dead end section of pipe, which is horizontal, but I am able to push this down to an angle sufficient (I'd have thought) to expel the air. I take it by your definition this is what you mean and that you expect this to be full of air for the condition to be present?
If this dead leg is impossible to purge then I'll just have to wait till I can get to the tee to modify the pipework. But at the moment there is too much destruction waiting to made good elsewhere.
I mean a part of the HW pipework which has not flow through it and thus can harbour air. A way you can get the air out of a 'dead' branch is to fit a quarter-turn service valve (aka Ball-o-fix) which you can use to flush out the branch into a bucket/bowl/tray thus expelling any air.
Yeah of course, I'm juggling 20 jobs, my only excuse for being daft.
Ed,
Can I ask what you mean by 'poorly clipped pipework' in laymans terms?
Thanks
Stuart
Pipes that visibly move in repsonse to pressure variations, in this case caused by turning taps on or off.
I have now solved my three dead legs by putting valves on the end and then bleeding air. (Thanks for the tip!) The combi boilder now does not fire when I use the cold water system.
However, the boiler still seems to fire for a couple of seconds every so often (haven't timed it but it seems to be about every hour).
My only explanation is that this is the pre-heat function keeping a little reservoir of water warm. Am I correct? If so, does anyone know how to turn this functionality off on a Glow-worm CXI combi??
Thanks
J
Provided we are talking about a model with GCN 47-047-23/24/27 a GW nn CXi Combi then look in the manual you'll see what to do to stop the preheat function?
a classic case of RTFM......Thanks Ed, I found it and it works.
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