Central heating control, any errors?

ericmark · 16 Jun 2019

I have worked out the above for my central heating, pump and valve for main house plus pump and valve for flat, and the domestic hot water is thermo-syphon.

Idea is domestic hot water will run boiler but not any pumps, and once the cistern is satisfied then the boiler will turn off, unless there is also a demand from main house thermostat, in which case boiler and pump will run, domestic hot water will clearly still be heated, but this is not a problem.

The flat heating will only work if the boiler is already running, however since the flat is smaller than main house and more sheltered it is unlikely the flat will need heat when the house does not, so that should not be a problem.

The original system had no valves and not any thermostat for main house, the plumber is fitting valves, after doing tests which showed central heating was thermo-syphoning and or having water forced around it in reverse direction, so it needs valves so I can heat water without heating house. I don't want a pump running if the valve is closed, so micro switch in valve works pump.

I think it's OK as shown, but I am not perfect so can anyone see any errors?

ericmark · 17 Jun 2019

Found one error new circuit

Are there any more I have missed?

ericmark · 17 Jun 2019

Slight change thinking of using Nest gen 3 and just time for domestic hot water for moment and see how it goes.

ericmark · 18 Jun 2019

This is the basic intended plumbing, there will be header tank etc. But this is the basic way it is to be plumbed up.

SimonH2 · 18 Jun 2019

That looks OK to me, as best I can read it on a small screen.

ericmark · 19 Jun 2019

Had to rethink to use existing cables between main house and flat, and between flat wall and cupboard at side of boiler where pumps and motorised valves are to be housed. So 4 wiring points new Nest 12 volt thermostat goes to old programmer location and a simple block connector connects cable from thermostat to cable to flat, the old FCU will become redundant and programmer replaced with a JB.

Then on flat wall old supply wire one to boiler becomes supply wires to new thermostat, and the second supply which powered the wireless thermostat receiver will now power whole boiler. So Honeywell wiring centre, heat link and flat thermostat all together on the wall.

Again old cables reused to old wiring centre to power the motorised valves and pumps in a cupboard at side of boiler.

Final plan completed today, tomorrow will start to wire up.

SimonH2 · 24 Jun 2019

The block with the solid blue terminals - is that the Nest unit ? With the two switches representative of it's relay outputs ?
Assuming yes, then it all looks OK now I'm able to follow it on a larger screen.

ericmark · 25 Jun 2019

Yes the blue terminals are the Nest, still waiting for plumber to fit valves, but with bridge 5 to 6 is does seem to work, but without motorised valves upper floor radiators get warm when set to DHW only.

FiremanT · 26 Jun 2019

ericmark said:
View attachment 166181 This is the basic intended plumbing, there will be header tank etc. But this is the basic way it is to be plumbed up.

Do the arrows on the pumps actually indicate direction of flow ? If so, t is circulating in the wrong direction. Are all of the pipes existing? Your post talks of both future and present tense

ericmark · 26 Jun 2019

Arrows are wrong direction, sorry missed that, all pipe work existing just adding motorised valves with each pump as pump when not running allows back flow and thermo syphon. And without motorised valve it would need a relay.

Some where from the cistern we have expansion and fill pipework, the problem is not sure exactly where this pipe work connects, the plumber advises that to add a motorised valve to domestic hot water we could in error interrupt the expansion and fill, and also there is no run on with boiler which with thermo syphon it does not need, so safer to retain DHW with no motorised valve, have considered a thermostat on the tank, but it would only do anything in summer, and now I can have ½ hour a day domestic water heating instead of original 3 hours minimum time, not sure worth the effort in wiring up tank thermostat?

JohnW2 · 26 Jun 2019

ericmark said:
... just adding motorised valves with each pump as pump when not running allows back flow and thermo syphon.

Have you actually experienced that, or are you just talking 'theoretical'?

My CH system has two pumps. One feeds multiple motorised valves (for different zones) but the other (plus a relay) serves just one (large) zone, with no MV. However, I've never noticed any significant flow through that latter pump when it is not running (but the other pump, hence also boiler, is running).

Kind Regards, John

ericmark · 26 Jun 2019

Getting back flow no question.

ericmark · 27 Jun 2019

Well I seem to have a further problem, got home last night, put hand on radiator and warm, put hand on input to cistern nearly burnt myself, went into flat where boiler is and it was running, turned off on isolator, then on and restarted so off to check this morning, dropped tail to boiler clearly don't want it running in this weather, powered up and tested and no supply to boiler reconnected boiler all seems A1 again.

Did check software and it said boiler has not run, did wonder it temporary wire caused it to latch, but switched off/on so any latch would have been lost, so my thought is.

Home/Away Assist
Automatically turn off when no one’s at home?
You can save energy by turning off the hot water when no one’s been home for 48 hours. Nest will return to your schedule when it notices that you’re back home.

Could this have switched on water heating when I got home? However the web page control said all not running, or had the contacts in rely stuck, if so need to return under complaint.

I am beginning to wish I had never got Nest, the help on web takes me to USA based adviser where they have a different version of Nest able to cool and heat with no heat link, they gave me a toll free number to ring, clearly in USA and I am not convinced it would be free from UK.

I don't know how long the heating had been running for, it may have switched on at 7:00 am and been running from then, thermo syphon only makes radiators warm not hot, and the TRV will stop many from heating up. And bathroom manually turned off, but now I don't trust it.

SimonH2 · 27 Jun 2019

Hard to diagnose after the fact. I'd be tempted to leave it and see if it happens again - if it does, then get test lamp out and see what's making it run before resetting it.
Had something similar with out heating a few weeks ago - we've only got a basic programable stat at the moment. The temperature was well above the setpoint so no heating should have been running, but the bathroom radiator and towel rail were hot. Boiler was running, but was OK after I power cycled it. I could only assume that Grand Master Glitch had been at it, and perhaps it had latched on when hot water last used (it's a combi

)

ericmark · 27 Jun 2019

Yes question has be risen could the fact paired to Energenie TRV heads be causing a software glitch? So as you say just go to see if it happens again, have wondered if worth running through the energy monitor so I can see when boiler fired up?

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Central heating control, any errors?

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