Viessmann firing when it shouldn`t

[iateyoubutler]

Afternoon all

I had my Viessmann 100W boiler fitted earlier this year (traditional system with vented cylinder etc), and so far I love it, it does the job nicely with no fuss which is more than I can say for the boiler it replaced!

Anyhow, one small problem I have noticed (occasionally) is that when either the heating or hot water shut down, the boiler will carry on firing for about 10 seconds or so which causes it to obviously overheat. The system is Y plan (I wired the electrics up myself years ago), with permanent and switched supplies going downstairs to the boiler, and indeed sometimes I`ve heard the pump stop - so the switched supply is going off as the boiler and pump are connected together, but yet the boiler will keep firing.

Doesn`t happen every time, maybe once every week or two but it doesn`t seem right to me. Has anybody come across an issue like this before?

Thanks

 

[picasso]

Might be backfeed voltage from the 3 port keeping the boiler firing but not the pump, I know w/bosch suffer from this and they supply a capacitor fitted across neutral and switched live to cure the problem, not saying this is your problem but cant see what else could be causing it.

 

[iateyoubutler]

Might be backfeed voltage from the 3 port keeping the boiler firing but not the pump, I know w/bosch suffer from this and they supply a capacitor fitted across neutral and switched live to cure the problem, not saying this is your problem but cant see what else could be causing it.

That`s an interesting idea, I`ll check that out. Would make sense. Thanks Picasso