Cylinder Thermostat Wiring

Could someone check the wiring on my evil plan to fit a cylinder thermostat to a system that doesn't currently have one fitted.

The wiring currently is:

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the pipework is a simple loop through the cylinder that extends through the heating when the value opens.

Can I just add the thermostat into the line currently shown between 16 and

3 on the diagram, and then join 8 to 3 to enable the heating to work when the cylinder thermostat is off?

Cheers

Steve

Reply to
Steve
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Fitting a thermostat can't achieve that, you'd need to change the plumbing. But I'm not sure theres much point in doing anything, what exactly is the problem?

NT

Reply to
meow2222

I struggling a bit to work out just what you've got. What is the valve - is it a motorised diverter valve which enables you to have CH or HW but not both at the same time?

If so, what you have is essentially a W-Plan system, and needs to be wired as per the W-Plan diagram shown at

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is it a gravity HW and pumped CH system? If so, you need to look at the C-Plan section of the Honeywell page referenced above.

Reply to
Roger Mills

at

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> Or is it a gravity HW and pumped CH system? If so, you need to look at the

AIUI he seems to have an older arrangement that is plumbed so that boiler output always goes thru HW first,. then may or may not go thru CH circuit. So HW temp is less well controlled than on modern systems.

I'm not clear what problem this is causing. Since an old cylinder will have relatively low transfer rate, the CH cct will still see hot water right away, though a bit below peak temp at first. If the HW cyl lacks a stat then I guess during HW only operation, the pump will keep running and the boiler stat will control the HW temp. Which seems quite workable.

NT

Reply to
meow2222

So what does the 'valve' do? I presume it would have to direct the output fom the cylinder either back to the boiler (HW only) or through the radiators (HW + CH). The mind boggles! Is it likely to be a single pipe CH system?

The problem with a system like that is that the HW will reach boiler temperature whenever the CH is on. So it's not possible to control the HW to

60 decC while feeding 80 deg C water to the radiators - you either have *very* hot HW or coolish radiators.

I presume that the cylinder stat would only be effective in HW-only mode? Whether the wiring arrangement suggested by the OP would work or not, I don't know - I guess it may need some additional relay logic.

Reply to
Roger Mills

The problem is that the boiler is on when it doesn't need to be, the boiler is in the garage so there is a large loop that will cool down quite fast and the boiler keeps trying to re-heat that loop. Even with the timing reduced it's still heating for no reason.

Why wouldn't fitting the thermostat in the manner I suggested work?(I have no experience in heating setup, and all the plan diagrams on the internet do not cover this system)

Steve

Reply to
Steve

I'm not sure exactly how the value makes the flow go through the raditors, it just opens the larger loop. I would have thought that the water would take the easier route back to the boiler and not go this extra route but it does.

I'm not worried about CH always heating the HW, thats fine, I just want to cut off the boiler when I don't need it for HW or CH.

Steve

Reply to
Steve

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