Can I use a Cylinder Stat on Pumped/Gravity Profile?

[JohnD]

Thanks, the existing Drayton controller has diferent HW and CH times and separate once/twice/on/off settings and Advance buttons.

Must I use the same controller as Honeywell show in their diagram, or are the connections standardised?

BTW I have a 28mm Drayton Cylinder valve with remote sensor bulb which I may fit as well, there is more room than round the boiler. However this does not stop the boiler cycling up.

 

[D_Hailsham]

Thanks, the existing Drayton controller has diferent HW and CH times and separate once/twice/on/off settings and Advance buttons.

Must I use the same controller as Honeywell show in their diagram, or are the connections standardised?

The answer is no in both cases your existing Drayton controller will do fine. You just need to identify which are the L. N. CH on and HW on terminals.

If your Drayton controller has volt free switching you will need to link the L to the switch. It will be explained in the instructions

BTW I have a 28mm Drayton Cylinder valve with remote sensor bulb which I may fit as well, there is more room than round the boiler. However this does not stop the boiler cycling up.

Then why bother? The important thing is to stop the boiler cycling and the unwanted circulation through the HW cylinder.

Note that the valve is in the return from the HW cylinder. If it was in the flow it could block the safety vent pipe.

 

[JohnD]

I have been studying the instructions (see pics below) which were left with the programmer.

This is, I hope very easy for someone who does it all day, but for a beginner like me a bit more caution is needed.

It appears to be a Drayton LP722

from the page headed "Installation" I see that HW ON is terminal (3) and CH ON is (4)

there are also terminals for HW OFF (1) and CH OFF (2)

I deduce that I connect the Cylinder Stat "Call" wire to (3) and the Cylinder Stat Satisfied to (1), and the "permanent live" supply to the cylinder stat to (L). The Cylinder Stat does not have a Neutral connection. (the one I bought is a Landis & Gyr RAM1 and looks extremely simple.)

a couple of things I wonder about:

There must be something causing HW to be permanently on with no cylinder stat, and presumably I have to remove whatever this is - a link, or switch?
it is currently installed as "Gravity HW, Pumped CH, room stat" and I understand there is a switch round the back that will be set to "G" (I have not taken it off the plate yet)
The instructions say that in this configuration the CH will not come on unless HW is on. But will the Cylinder Stat, when satisfied, turn HW off and therefore prevent CH from running? If so should I just turn the switch to "P"?

The diagrams for Cylinder Stat are for "Mid Position Valve" configuration and "Spring Return Valve" configuration, neither of which I have. I want to leave the HW on gravity, but turn it off when Cylinder Stat is satisfied.

Have I missed anything?

TIA


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[DP]

Gravity HW results in only boiler running. For central heating, only pump runs (through a thermostat usually). Pump running by itself will not heat the house so an internal ling within the programmer activates the boiler to heat water that pump pushes to rads (natural movement of water to cylinder is often effected when pump is running resulting in poorer HW heatup)

If fitting a thermostat on the cylinder, you have to maintain isolation between boiler and the pump. John, email me for diagram of how you can achieve results just by fitting a cylinderstat. Do be aware however, boiler will still cycle during HW mode as boiler can generate heat faster than cylinder can sink until target temperature has been achieved when all falls silent.

 

[JohnD]

Thanks!

You have mail...

 

[JohnD]

with all your help, especially DP (thanks, Danny) and Drayton who sent me their unpublished wiring diagram, I think I have now puzzled out why I couldn't understand how to make it work.

the logic I want is

1) if HW timer is "ON" and HE Cylstat is "Call", Fire boiler

2) If CH timer is "on" and Roomstat is "ON", fire boiler and run pump

3) Else, all off

So I have two conditions where I want to fire the boiler, only one of them runs the pump.

the boiler only has one switched Live.

So I can't connect the two command SLs together, or both HW and CH would always be on if either of them was on.

What's needed is another changeover switch which i had not envisaged in my faulty concept.

the Drayton diagram includes a 2-port valve with end switch, so that when HW is on, it connects HW SL to boiler, and when HW is off it connects CH demand SL to boiler.

the 2-port valve has an additional purpose of preventing primary flow to cylinder when cylinder is satisfied, which in my original concept I had considered unnecessary since I expected to use a thermostatic valve at the cylinder.

Probably easy to you guys who do it all the time and I realise now that you were telling me and I didn't grasp the importance of the zone-valve switch

Fleabay is now looking for a modestly-priced 28mm 2-port with end switch for me