s-plan pump overrun

[algo]

Hello,

I had to tidy up some wiring on my S-plan system yesterday - the boiler has an overrun and we use a megaflo 120 for hot water. The wiring for the pump overrun is done so that the pump runs with the only circuit being the closed loop with bypass (automatic bypass fitted at 0.3bar) - both the heating and hot water valves are shut during this phase. This all works fine.

I was wondering though whether anyone thought it might be a good idea to write a simple logic board so that the CH zone valve would open during this phase so that the overrun circuit would include the rads. This would surely make the overrun duration shorter, and it would use the heat in the closed loop.

It needs a logic board as clearly you can't just use the overrun signal to open the valve or it will switch the boiler on again.

I think that's how it is on a Y-plan but not totally sure. I'm not sure it's worth it and whether it would benefit the boiler or not. Any expert opinions gratefully received!

 

[matt1e]

Not sure about a "logic board" but yes you do req some control logic and yes it's pretty easily achievable using off the shelf components.
a three port doesn't need the same logic as normally it will always have a port open

Matt

 

[algo]

Hi Matt,

thanks for the reply - would you say it's worth doing though? Is there already a component that exists to control this? Sorry I had a look but didn't find anything immediately - perhaps should have looked closer. I was going to use a DPDT and a SPST relay - that's enough to give the right logic so that the CH zone valve switches on without switching the boiler on.

 

[matt1e]

Well discounting PLC's I'm not aware of any dedicated controllers but yes a couple of relays would do it

Matt

 

[algo]

Thanks again for your help,

PLC or smart relay would be a good option but a bit pricier. Still want to know if people think it's worth it, or whether it's ok just to have the overrun circuit around the bypass...

 

[picasso]

You don't need a logic board, if you want to dump the heat into the rads just put the bypass across the central heating two port valve.

 

[algo]

Thanks for the reply.

I can see how physically changing the pipes would work - that's another option. Thanks again

 

[Norcon]

If you change the by pass valve unto the zone valve then you have no by pass from flow to return which your boiler MI's might be calling for!.

An off delay timer relay will do what you want for £30 quid.

 

[algo]

Hello,

what I interpreted was to use an automatic bypass valve to bypass the zone valve for the rads - I have a non trv rad and thermostat so there'd always be a loop for the bypass circuit. Not sure whether this is a good idea or whether to leave the existing closed loop bypass.

Thanks for the info on the relay - that's a good idea too.

 

[matt1e]

An off delay timer relay will do what you want for £30 quid.

He's not on about adding pump overrun Norcon, he already has a timed off delay inbuilt for that, it's logic switching he requires mate

Matt

 

[picasso]

The ch zone valve isint normally bypassed because the customers complain of rads warming in the summer, if your going to change the pipework bypass the hot water zone valve, the heat is then dumped into the hot water cylinder (not allowed on unvented cylinders)

 

[Norcon]

Yes but I meant applying the off delay to the zone valve, timed to match the over run timer.

 

[matt1e]

Yes but I meant applying the off delay to the zone valve, timed to match the over run timer.

wouldn't work on its own mate, you still need control logic to isolate the valve micro switch
ie control logic would be
no demand for hot water or central heating and pump runnng = isolate boiler demand (valve micro switch) and open ch valve for duration of the pump running

easy (expensive) via BMS/plc but you could hard wire it with a couple of relays too as far as I can see

Matt

 

[hazetimesfive]

some people have too much time..

 

[Agile]

Those kinds of circuits are best built into Tupperware boxes as they look acceptable and meet the IP44 splash proof requirements!