S Plan with Stove + Controls

[Hants-Spark]

I'm after a bit of advice from you heating engineer experts.

I have wired many boilers previously but never to include a wood burner

I have been asked to wire an S plan heating system, no problem with this.
They have also installed a wood burner with a gravity rad and twin coil cylinder.

They have fitted a N/O valve on the return of the stove, low level and high level pipe stats.

Now this is where I'm struggling to see what they want.

N/O valve to close when boiler is running unless the L/L stat makes and opens said valve.
H/L stat opens Heating valve and runs pump but does not fire the boiler.

I can see how to wire the H/L stat to operate v/v, pump via relay, I can see how to include N/O v/v part but just cant get my head around the L/L stat and opening v/v or even why its required.

Any ideas would be greatly received

 

[Leesparkykent]

I'm after a bit of advice from you heating engineer experts.

I have wired many boilers previously but never to include a wood burner

I have been asked to wire an S plan heating system, no problem with this.
They have also installed a wood burner with a gravity rad and twin coil cylinder.

They have fitted a N/O valve on the return of the stove, low level and high level pipe stats.

Now this is where I'm struggling to see what they want.

N/O valve to close when boiler is running unless the L/L stat makes and opens said valve.
H/L stat opens Heating valve and runs pump but does not fire the boiler.

I can see how to wire the H/L stat to operate v/v, pump via relay, I can see how to include N/O v/v part but just cant get my head around the L/L stat and opening v/v or even why its required.

Any ideas would be greatly received

This may be of some help. Page 11,12 and 13 on post below...for some reason wouldn't let me edit and post link here.

 

[Leesparkykent]

http://shop.euroheat.co.uk/ImgShare...Boiler_Management_System_Centre_1_Low_Res.pdf

 

[Hants-Spark]

Thanks for this, much appreciated.
I'll have a good look through tomorrow and see if I can get my head around it. I'm sure it's fairly simple once I fully understand what they are trying to achieve.

 

[aesmith]

I can see how to wire the H/L stat to operate v/v, pump via relay, I can see how to include N/O v/v part but just cant get my head around the L/L stat and opening v/v or even why its required.

Any ideas would be greatly received

A stat on the return to a solid fuel boiler normally operates to inhibit the heating pump if the return temp is too low, to protect the boiler (gravity circuit would continue to flow, so the valve must be open in this state).

In your case you want an additional interlock - close that valve if the boiler's running and the stove's not lit (otherwise you circulate heated water through the stove). Can you map out all the different states, and see how each valve should operate in each state? Then the challenge is how to make the various control inputs and stats give that end result. I can't quite see how you can get the correct behaviour for the N/O valve just from the one thermostat.

The solid fuel and gravity circuit also needs to be safe if the power's off.

 

[Hants-Spark]

Thank you both for your replies, I've done a drawing which I'm hoping is correct although when I scan it, it saves as a PDF and cant seem to load it onto here.

Anyway what I've come up with is, a standard S plan through a relay on the N/C terms, a perm feed to the H/L stat then returning to fire the coil of the relay, the N/O contacts then operate the Heating valve and pump thus dispersing the heat around the circuit.
The L/L stat comes off the N/O contacts then onto the stove valve, thus closing the valve and preventing cold water through the stove when the boiler is running.


Hope I've explained it OK, any questions or comments feel free.

 

[Leesparkykent]

Thank you both for your replies, I've done a drawing which I'm hoping is correct although when I scan it, it saves as a PDF and cant seem to load it onto here.

Anyway what I've come up with is, a standard S plan through a relay on the N/C terms, a perm feed to the H/L stat then returning to fire the coil of the relay, the N/O contacts then operate the Heating valve and pump thus dispersing the heat around the circuit.
The L/L stat comes off the N/O contacts then onto the stove valve, thus closing the valve and preventing cold water through the stove when the boiler is running.


Hope I've explained it OK, any questions or comments feel free.

This could come in handy. http://www.gledhill.net/pdf/torrent range issue 2.pdf

 

[aesmith]

On that drawing, which is the stove return pipe stat, and where does V3 fit in the pipework?

 

[Leesparkykent]

On that drawing, which is the stove return pipe stat, and where does V3 fit in the pipework?

here's the pipework/component layout. Obviously the solar thermal can be ignored.

 

[Leesparkykent]

This is for a gledhill thermal store but the OP could adjust it to his requirements but good as a reference to work off.

 

[aesmith]

The valves and stats don't seem to be in the same locations, if I follow correctly.

The design decision for the OP is whether the stove, or the boiler takes precedence. Then the right interlocks need to be in place.

In particular that N/O valve in the gravity circuit return is a concern, it needs to be open any time the stove's burning irrespective of what the rest of the system is doing. So that can't just be closed when the boiler's running. Nor do I think it can be controlled by the stat on the return, unless that is set really low - in which case it wouldn't be correct to inhibit the heating pump until the gravity circuit's up to temperature. I'm thinking you may need a separate stat for the purpose, and it would need to be somewhere where pumped flow from the boiler wouldn't influence it.

 

[Hants-Spark]

Thanks again for the info, it is pretty much the same as I'd drawn with minor changes to suit the system I'm doing so hopefully it should be ok, you've both been a great help, cheers.

 

[Hants-Spark]

The valves and stats don't seem to be in the same locations, if I follow correctly.

The design decision for the OP is whether the stove, or the boiler takes precedence. Then the right interlocks need to be in place.

In particular that N/O valve in the gravity circuit return is a concern, it needs to be open any time the stove's burning irrespective of what the rest of the system is doing. So that can't just be closed when the boiler's running. Nor do I think it can be controlled by the stat on the return, unless that is set really low - in which case it wouldn't be correct to inhibit the heating pump until the gravity circuit's up to temperature. I'm thinking you may need a separate stat for the purpose, and it would need to be somewhere where pumped flow from the boiler wouldn't influence it.

From what the heating engineer has said, the valve needs to be open at all times unless the boiler is running, except when the low level stat operates and closes it to prevent cool water being pumped through the stove. Does this go along with what your thinking??

 

[aesmith]

From what the heating engineer has said, the valve needs to be open at all times unless the boiler is running, except when the low level stat operates and closes it to prevent cool water being pumped through the stove. Does this go along with what your thinking??

Not quite. If this was a pure solid fuel system, the low level stat on the return would inhibit the heating pump, but not the gravity circuit. The gravity circuit is needed any time the stove's lit, otherwise there's no where for the heat to go, and without flow I'm not sure you could rely on the stat on the return closing.

 

[Hants-Spark]

If I'm understanding you correctly the high level will deal with any heat build up, once the h/l stat operates it shuts the boiler off, if running, opens the heating valve and runs the pump or am I misunderstanding you?

 

[aesmith]

I think I see what you mean. If I understand you correctly the sequence would be ... heating running from boiler, so the N/O valve is closed by the interlock from the boiler controls. Now someone lights the stove. There's no gravity circulation because that valve's closed, so heat builds up in the stove boiler. If your high level stat is close enough to the stove it will receive this heat as well, and close. This breaks the link to the low level N/O valve which then opens and allows circulation through the stove.

That could work as long as that high level stat does in fact sense the stove boiler temperature when there's no flow.

Solid fuel operation only you want the pump be operate only when the gravity return (low level stat) is up to temperature.

 

[Hants-Spark]

You've got it in one, thanks for all the input its been a great help.

 

[PEG]

I think I see what you mean. If I understand you correctly the sequence would be ... heating running from boiler, so the N/O valve is closed by the interlock from the boiler controls. Now someone lights the stove. There's no gravity circulation because that valve's closed, so heat builds up in the stove boiler. If your high level stat is close enough to the stove it will receive this heat as well, and close. This breaks the link to the low level N/O valve which then opens and allows circulation through the stove.

That could work as long as that high level stat does in fact sense the stove boiler temperature when there's no flow.

Solid fuel operation only you want the pump be operate only when the gravity return (low level stat) is up to temperature.

Hi,just crossing the tees'...just ensure that NO valving,manual or electric ,restricts circulation. This can be assisted or biased,but never restricted.

The default position,regardless of setting,malfunction or electrical mishap,should always allow gravity operation and dumping of output.

I have come across many systems,where boiler stoves have been shoe'd in,and things are groovy,till a fuse blows,or a pump/valve fails...and then it's thunder time...:tounge_smile:

 

[Hants-Spark]

Thanks for the input PEG