Heating Control Options

The attached diagram is a representation of my hot water & central heating system.

In case it's relevant the boiler is a Vokera mynute 14e and the existing motorised valves are Myson MPE222's.

The problem at the moment is that the two room thermostats are not working correctly. I had also planned to add a different timeswitch to give me 7 day control and boost functionality but I never got round to it so that's in the mix too.

So I basically need to change the timeswitch/programmer and the room thermostats. Seeing as I'm going to this trouble I'd like to end up with some decent level of control so as to use the heating as efficiently as possible.

I was thinking of getting the following:

2 * programmable thermostats
1 * 2 channel programmer

The idea being that I can set up the hot water channel just to switch the boiler on/off when necessary and that either room thermostat will turn on the relevant motorised valve and switch the boiler on/off through the central heating channel which will be left on constant. I'm aware that, because of the system design, I will get the hot water on when the heating is on but I'm not certain if the extra work involved in adding a three way motorised valve is worth it.

Is this a good way of doing this? Anyone have any suggestions/opinions?

Why not put another zone valve in the HW cylinder circuit, controlled by a cylinder stat. This will mean the HW temperature is independent of the boiler temp. However, you may need to install an automatic bypass valve

You only need a single channel timeswitch for the Hot Water side.

What you have is called an S-plan Plus layout



The wiring is like this, with an additional heating circuit



Also have a look at Honeywell Application Guide 110 - S plan with programmable thermostat

D_Hailsham said:

Why not put another zone valve in the HW cylinder circuit, controlled by a cylinder stat. This will mean the HW temperature is independent of the boiler temp. However, you may need to install an automatic bypass valve

You only need a single channel timeswitch for the Hot Water side.

What you have is called an S-plan Plus layout

The wiring is like this, with an additional heating circuit

Also have a look at Honeywell Application Guide 110 - S plan with programmable thermostat

Click to expand...

Not a bad idea but one problem I have is that the cylinder is encased in solid insulation and I can't install a cylinder thermostat.

tkk said:

Not a bad idea but one problem I have is that the cylinder is encased in solid insulation and I can't install a cylinder thermostat.

Click to expand...

If you mean polystyrene insulation, that's no problem. You just use the thermostat as a template and cut away the insulation with a stanley knife. It's the way everyone does it.

Yes it's encased in polystyrene. Cutting away the insulation I can manage

Can you clarify what you mean by saying I may need to fit a bypass valve? Is this so that the pump can still circulate the water after the various zones have switched off to avoid damaging the boiler? Would this simply be a link between the flow and return with the bypass valve in the middle?

Am I right in saying that I set up the HW so that when the timeswitch turns on at the appropriate time this gives power to the cylinder stat which, if necessary, turns on the new HW motorised valve which in turn switches on the boiler?

tkk said:

Can you clarify what you mean by saying I may need to fit a bypass valve?

Click to expand...

You will not need to bother about fitting a bypass as your boiler has an internal one.

The purpose of a bypass is to provide a path for the water to flow through when all the motorized valves are closed and the boiler is cooling down.

Am I right in saying that I set up the HW so that when the timeswitch turns on at the appropriate time this gives power to the cylinder stat which, if necessary, turns on the new HW motorised valve which in turn switches on the boiler?

Click to expand...

Correct. If the HW is below temp (60C is recommended) the stat will open the valve, which will close the internal switch and fire the boiler.

It's all shown in the S plan diagrams I posted. As you have two CH zone valves you will need to duplicate the CH part of the diagram. Unfortunately Honeywell have not published an S-plan wiring.

That's great.

Am I right in saying that Honeywell would be a good brand to go with here? How aboud Sunvic or one of the other brands?

tkk said:

That's great.

Am I right in saying that Honeywell would be a good brand to go with here?
How aboud Sunvic or one of the other brands?

Click to expand...

Honeywell are very good. It's what I use and I have had no problems.

Drayton are prone to problems, Danfoss are expensive and Sunvic is at the cheap end of the market.

Thanks for your help

how did you get on with this

also have vokera that isnt mains fed and constantly cutting out, no filling loop

attic fed will only give you 0.5 bar pressure probably why no gauge in hot press