S-Plan central heating - bypass microswitch?

[PedroKTFC]

I have Drayton motorised valves for my central Heating and hot water in an S Plan configuration. However, I have had several failures of the microswitches in these valve where they've not switched off and so left the pump and boiler running. This leads to the boiler over heating and so tripping and needing to be reset (imagine if it didn't trip??!!).

So I was wondering of I could bypass these and switch on the pump and boiler directly when the timer/thermostat call for heat? I really don't see any benefit in going via these microswitches.

 

[mainline]

I have Drayton motorised valves for my central Heating and hot water in an S Plan configuration. However, I have had several failures of the microswitches in these valve where they've not switched off and so left the pump and boiler running. This leads to the boiler over heating and so tripping and needing to be reset (imagine if it didn't trip??!!).

So I was wondering of I could bypass these and switch on the pump and boiler directly when the timer/thermostat call for heat? I really don't see any benefit in going via these microswitches.

What about the situation where the valve fails to open. ?

The boiler shouldn't overheat and cause a trip, it should simply shut down either via room stat, immersion stat or internal boiler stat.

 

[PedroKTFC]

What about the situation where the valve fails to open. ?

The boiler shouldn't overheat and cause a trip, it should simply shut down either via room stat, immersion stat or internal boiler stat.

But what's the difference between that and the valve closing but the microswitch not switching off?

The boiler does overheat: the valve closes but the microswitch fails, meaning the pump and boiler continue to run, water doesn't circulate but the boiler is burning gas until it overheats and trips. At this point the boiler no longer fires and the pump runs forever against a closed valve. Bonkers!

 

[mainline]

But what's the difference between that and the valve closing but the microswitch not switching off?

The boiler does overheat: the valve closes but the microswitch fails, meaning the pump and boiler continue to run, water doesn't circulate but the boiler is burning gas until it overheats and trips. At this point the boiler no longer fires and the pump runs forever against a closed valve. Bonkers!

You need to know that the valve is actually open before the boiler and pump starts.

Generally, the switches are reliable, It may be worth adding a contactor to switch the pump instead of directly from the microswitch.

Is the failing of the micro switches due to contacts fusing together, or is it a mechanical one ?

 

[PedroKTFC]

You need to know that the valve is actually open before the boiler and pump starts.

Generally, the switches are reliable, It may be worth adding a contactor to switch the pump instead of directly from the microswitch.

Is the failing of the micro switches due to contacts fusing together, or is a mechanical one ?

Failure just seems to be a mechanical one.

I realise that the valve is open before the boiler and pump start but they're closed if the micro switch fails. It just seem less likely that the motor or valve will fail than the micro switch, at least in my experience of my one house.

 

[Resu]

If you bypass the microswitches you'd need to incorporate a couple of contactors or relays to avoid each zone back feeding each other. The microswitches stop this as well as only firing the boiler/pump when the valve is open.

A different solution would be to switch out the brand of valves to another like Danfoss or Honeywell.

Would also be worth considering getting a bypass fitted so that in the event of a similar failure the pump isn't pushing against closed valves.

 

[PedroKTFC]

If you bypass the microswitches you'd need to incorporate a couple of contactors or relays to avoid each zone back feeding each other. The microswitches stop this as well as only firing the boiler/pump when the valve is open.

A different solution would be to switch out the brand of valves to another like Danfoss or Honeywell.

Would also be worth considering getting a bypass fitted so that in the event of a similar failure the pump isn't pushing against closed valves.

But if the microswitch fails and doesn't switch off, there is no way of switching off the pump (and boiler but that trips). I can turn down the thermostat/turn off the hot water (depending on which has failed) but the pump will merrily carry on till the cows I don't have come home! That seems utterly bonkers to me.

 

[Simon47]

But if the microswitch fails and doesn't switch off, there is no way of switching off the pump (and boiler but that trips).

That seems utterly bonkers to me.

That comes down to "if something fails, things don't work properly". Yes they can fail, but absent faults elsewhere they are reasonably reliable.