Flush the loo - boiler runs!

[ec145]

We've had a new combi boiler fitted a few months ago, so our system has gone from a stored water system to a direct mains fed system. Just noticed that when the toilet is flushed, the boiler sparks up (as per turning on a hot tap) and then goes off, but keeps running for a little bit. The toilet fills up in a few seconds.
How do I stop it?
I've already tried half closeing the isolating valve to the loo to restrict the flow, but it makes no difference.
Cheers
Pete

[rosebery]

Check plumbing. It sounds as though your installer has the loo feed on the DHW rather than cold!

Cheers

[ec145]

Thanks Rosebery, but I'm positive the loo is plumbed into the cold water. I can easily trace the line round the bathroom, bath - basin - loo. The hot water only goes to the bath & basin.
Should have made it clearer, the boiler only comes on when the toilet is full and the feed stops.[/list]

[rosebery]

Siunds like ytou have some pressure issues with your system so that whe the toilet fill valve closes you get a pressure wave causing the flow switch on the boiler to operate. Water hammer without the hammer! Open up the ervice valve onthe loo feed again and try throttling back your mains stopcock a little and see if that stops it.

In any event I think you should invite your installer back to have a look at it (at his cost mind as its only been a couple of months) as well as it ain't right!

Cheers

[Tw1zzle]

Hi Guys
I got the solution to the problem. I have just done some plumbing work in my bathroom and found every time i shut off the cold water tap the boiler would fire. I did a lot of research and found that fitting a one way or check valve just before the boiler has done the trick. You can then open teh main stop cock fully and not worry. The reason for teh boiler firing is that you are getting a reverse flow and no matter how small it will trigger the boiler to fire. Hope this helps.
Twizzle