Vaillant 418 going a bit wild

[paleo]

After 10 years a stuck microswitch in one of the 2 ports would be more likely the problem.

Thanks. What are ports please?

 

[Mottie]

Thanks. What are ports please?

2 port motorised valves.

 

[Mottie]

Thanks. If all goes according to plan, the electrician and the heating engineer will come by tomorrow. I'll run that past them,

Well, how did it go?

 

[paleo]

Well, how did it go?

Hi, I showed the electrician your photograph and mentioned what you said. He said my boiler is older than yours, going by the photograph, but the problem was very similar in that a link that should not be there had been left in place. Also, the pump had been wired up in a rather unusual way. He rewired things and removed the rogue link and as far as I can see all is well: the boiler fires when it's supposed to, the temperature rises to the set temperature, then the boiler goes into anti-cycling mode for 5 minutes or so while the pumpt keeps running. It goes on doing that until the room temperature set on the room thermostat is reached. So far no wild firings.

Thanks for your help; I don't think they would have had a look at this link without your input.