boiler coming on when toilet is flushed

[bfguk]

baxi combi 133he plus
when the toilet is flushed or cold water tap turned on the boiler kicks in any ideas why?
thanks

 

[scatmanjohn]

Hi.. This can occur when the water "bounces" (for want of a better word).
When you turn on a cold tap or flush the bog it can cause movement of the water in the boiler which can operate the flow switch.
Not sure on the type of flow switch on this boiler but it sounds to me like thats the problem.
To stop it happening you can fit a non return valve on the cold water pipe that enters the boiler, however most manufacturers say you must fit a small expansion vessel between the boiler and the valve.

Do's anyone know of any other way to stop it happening?

 

[compheat]

As the scatman say,s its due to pressuse fluctuation

 

[John.B]

Do not fit a non return valve on the cold entering the boiler. There are cases of the internal pipe-work on combi boilers splitting open when water meters with non-return valves have been fitted on the cold mains. To fit a non return valve so close to the boiler will cause an even bigger risk of damage. Boiler manufactuers recommend a mini expansion vessel to be fitted as Scatmanjohn recommends.

 

[jackohelp]

or the toilet fill has been connected to a hot water pipe. It may have happened!!!!

 

[PEDANTICVINDICTIVEMAN]

Most likely going to be a dead leg (capped off pipework) somewhere in the property causing this.

 

[bfguk]

thanks for the advice.
the toilet is definately not conected to the HW system.
the problem occurs from operating a cold water tap also. there is no non return valves or water meters in the system. it would appear to be some sort of warter bouce.
so i guess a expansion vessel could solve the problem
thanks

 

[scatmanjohn]

Hi..

I think you misunderstood some of the advice.
A non return valve would stop the "bounce"
If a non return valve is fit then a mini expansion vessel must also be fit to take up any expansion after a hot water demand.
This expansion usually just passes back into the cold main but with a non return valve fitted this can't happen.
Get in touch with baxi before fitting one to see if it is acceptable.

 

[bfguk]

it is ok according to the manual to fit a non return valve along with a expansion vessel.
but after further searching on te net the dead leg sounds like it could be the problem. its just a matter of finding the leg.