vaillant 831 - keeps firing

[philpepper]

I have a problem with the above combi boiler. Whenever a cold tap is turned on - then off, or after the loo has been flushed, the boiler briefly fires up.

I think its got to do with pressure but i dont know how to cure it. There are no dead legs on the sytem. Only thing recently added has been the installation of a thermostatic shower. Could that be the cause.

Any help in sorting this out would be appreciated.

Phil

 

[gas4you]

If you are 100% sure there are no dead legs anywhere, then you could try non-return valves in the hot and cold to the shower.

 

[undercover]

agree with gas4you's advice... Check that you have no dead legs on the system so cut back any pipework that no longer feeds anything on your system.

you could add non return valves to the hot and cold supply to the shower and maybe also to the "loo". I bet the loo causing the problem is in the same room. I was called to a similar problem where both the combi and loo were in a utility room. A check valve on the supply to the loo stopped it.

Same applied to the tap (check valves on hot and cold)as i bet its a mixer made in europe...

Some boiler manufacturers are now recommending that a pressure reducing valve and mini expansion vessel are installed..

 

[David937]

Also, try setting d.88 to 1.

 

[undercover]

Also, try setting d.88 to 1.[/quote

that means the OP has to access the 2nd diagnostic level

 

[David937]

Indeed.

 

[philpepper]

sorry, but i ain't got a clue about acessing diagnostic levels.

did what you said to do "undercover" and added a check vale to the loo in the utility room which is where this boiler has beeninstalled. sorted out now..

by the way what is settin d.88 to 1. what does this do to the boiler???

 

[David937]

To change d.88 to 1 you press the i and + buttons simultaneously then use the + and - buttons to get to d.97, once you have got to d.97 press i and use the + button to get to 17 then hold down i to confirm, scroll to d.88 press i and change the 0 to 1 and hold down i to confirm, finally press i and + buttons to leave the diagnostic mode.

I am not 100% sure what d.88 does but I think it is to set the minimum flow required to operate the boiler in DHW mode.

 

[glasgowgas]

by the way what is settin d.88 to 1. what does this do to the boiler???

I am not 100% sure what d.88 does but I think it is to set the minimum flow required to operate the boiler in DHW mode.

first time i have ever seen a post that truely should be in the Combustion Chamber