Ignition light on & off while cold and hot water are mix

[karine]

I am trying to plumb everything myself and nothing goes as easy as planned. I have just fixed a mixer tap (not thermostatic) for the use of bath and shower. I have now noticed that when I mix the cold and hot water, the ignition light on the combi boiler (Vaillant) goes on and off and when it comes on again the pilot light goes on. It is the same for the hot and cold taps in the kitchen and the washing machine (with hot and cold feed)- There shouldn't be any air in the system as I have already checked. The pressure and hot water supply is perfectly fine during a shower. Has anyone got any idea what the problem could be?

 

[Bahco]

Doesn't sound like you have any problem
The boiler is supposed to fire up because it is heating the DHW in the secondary heat exchanger.
If all your hot supplys are fine and working to correct temp what is your concern
Maybe I have read your post wrong but see what the other guys think

 

[karine]

Thanks for that but what I meant was that the ignition light was going on and off during a shower of 10 minutes approximately 12 times (every 15 secondes). Is that normal or is there something wrong with it ??

 

[ArtfulBodger]

That sounds very much like running the cold reduces the pressure via the hot taps to such a degree that the boiler cannot fire.

Try this; Run any cold tap anywhere, then turn on a hot tap - does this fire the boiler? If not, turn off the cold tap and does the boiler fire then?

If the answer is (no) and (yes) then I would suspect that you shouldn't have a combi boiler at all.

 

[kevplumb]

is your shower running cold ?

 

[karine]

OK I will try tonight the hot and cold tap test as you suggested. Will see what happens. Yes the shower is running perfectly fine. The pressure is great and the hot water is constant. So still no clue what the problem could be.
I was trying to find out a solution before calling in a plumber.