Boiler fires up when toilet flushes

[Aquariusplumb]

Been called out to a job. Baxi platinum combi fitted in airing cupboard next to bathroom. Green led for hw comes on when toilets flushing but not until cistern has filled up and ball valve shuts off. I thought straight away the new bathroom fitted has a pipe crossed to the wc but then I took the syphon out to constantly fill the toilet and boiler didn't fire up. When looking at boiler noticed pressure was down so topped that up and that knocked the green led hw on boiler so I'm thinking the pressure in the house is affecting the boiler and there's no crossed pipes! Any thoughts or suggestions??

 

[glenno1]

Is water warm in the cistern after filling

 

[Aquariusplumb]

No and the boiler never fires up even after letting toilet constantly fill for 10 mins. Led comes on as soon as ball valve shuts off

 

[glenno1]

Does pressure gauge drop when toilet is taking water

 

[Aquariusplumb]

No. Pressures fine just at first it was little low off customer bleeding rads before I got there

 

[glenno1]

You may have to trace the supply pipe back,because the boiler is supplying a demand for some reason,unless it is a boiler fault

 

[Aquariusplumb]

Problem is its a new bathroom and the floors just got tiled last wk. I dnt want to be taking up tiles if its not a new bathroom plus I know the plumber who fitted it and he's clued up and doubt he would cross pipes. The fact the hw led came on when I turned the filling loop on makes me think its nothing to do with the toilet. Is there a max cold water inlet pressure for a baxi platinum?

 

[garyplumb]

Try putting a flow restrictor in the toilet

 

[dontknowitall]

Is wc connected to the heating circuit?

The pressure will drop when water's removed from the heating.

 

[glenno1]

Your going to have to get a gs reg plumber in to check the boiler out

 

[Aquariusplumb]

No the pressure on heating is fine, hot water is fine, only issue is when cold feed to the toilet, filling loop gets turned off the led on boiler comes on. Boiler doesn't ever fire up. I am a gs reg plumber

 

[glenno1]

If pipes are fine and pressure is fine it must be something in the boiler

 

[dontknowitall]

Is wc connected to the heating circuit?

The pressure will drop when water's removed from the heating.

No the pressure on heating is fine, hot water is fine, only issue is when cold feed to the toilet, filling loop gets turned off the led on boiler comes on. Boiler doesn't ever fire up. I am a gs reg plumber

Oops! Sorry, I mis-read your initial post! :smile:

 

[SimonG]

Fit a check valve on cold feed to combi

 

[SimonG]

If the bathroom has just been done and the problem has just started is there a dead leg on the hot water side? Just enough water movement to trigger the flow switch?

 

[lame plumber]

stick a pressure reuducing valve on the incoming cold main and a hammer arrestor on the wc feed, sudden jolt when wc is filled will cause the boiler flowswitch to activate so reduce mains pressure and hammer arrestor will stop the jolt effect. fairly common problem on newer combis. I am presuming that a backflow preventor and expansion vessel have also been fitted already on the dhw side iaw manufacturers instructions to prevent the problem your getting

see section 6.8 para 3: http://www.baxi.co.uk/docs/Baxi_Platinum_Installation_Instructions2.pdf