Boiler problems

[TallJim]

I've been having trouble with my boiler. Due to my refusal to pay someone an stupid amount of money to fix it, I have tried a bit of DIY.

Basically I have replaced two of the circuit boards and the boiler now seems to work.

Unfortunatly the boiler only starts up when I manually open the Zone Valves. The times control box doesn't seem to have any effect on the system at all (although it does have power, and seems to be turning itself on and off at the correct times).

Does this sound like a problem with the control box, as the boiler and pump start up when I manually open the valves. Is the control box only responisble for opening and closing the zone values automatically ?

Thanks for any advice

[TallJim]

I've been having trouble with my boiler. Due to my refusal to pay someone an stupid amount of money to fix it, I have tried a bit of DIY.

Basically I have replaced two of the circuit boards and the boiler now seems to work.

Unfortunatly the boiler only starts up when I manually open the Zone Valves. The times control box doesn't seem to have any effect on the system at all (although it does have power, and seems to be turning itself on and off at the correct times).

Does this sound like a problem with the control box, as the boiler and pump start up when I manually open the valves. Is the control box only responisble for opening and closing the zone values automatically ?

Thanks for any advice

[Tony Bryer]

If it's a standard S-Plan system with two motorised valves (one for heating, one for DHW) then each valve has four connections. Two (L&N: brown/blue) go to the motor and open the valve when power is applied. The other two (grey/orange) go to a microswitch which closes when the valve opens: one of these two wires should go to a permanent (except when isolated) live, the other goes back to the boiler call for heat terminal.

If the system works correctly when you manually open either valve then the boiler side of the wiring all sounds OK. This would then suggest that power is not being delivered to the MVs when the programmer turns on and you need to follow through the circuit to see what is happening. MV motors do burn out, but the chances of both of yours failing together would seem pretty remote.

[TallJim]

Thanks a lot Tony, that make lots of sence. I think it is a S-Plan boiler (Vailant 112E), and it does has 2 MV's. I will try to follow through the circuit to see it I can find the problem. I assume if the MV's are both still working, then the most likely problem is the programmer ? Although I can't believe so many things went wrong at once.

[Set Square]

If it's an S-Plan system, have a look at the S-Plan diagram in

will see that the CH MV is fed from the programmer via the room stat. Similarly, the HW MV is fed from the programmer via the cylinder stat. Both valves have a pair of 'volt-free' contacts (i.e. electrically isolated from the motor feed). When a valve opens fully, these contacts close. One side of each pair of volt-free contacts is connected to permanent live. The other side is connected to the boiler and pump (or just the boiler, if the boiler controls the pump to provide pump over-run). So, when either or both circuits are demanding heat, the appropriate valve(s) should open and - in turn - switch on the boiler and pump.

So you need to trace the wiring for each circuit - from the programmer, through the stat to the motor - to see what is live when it should be, and what is not.

[Ed Sirett]

In between the timer outputs and the zone valves there may be thermostats on the wall and HW cylinder. as needed.