Control of Oil Boiler- Hot water

[nigelpcat]

I have a oil fired boiler with two pumps one for central heating one for the central heating. I want to fit a motorised valve so I can control the hot water temperature with a cylinder stat. Do I just put a valve in the hot water circuit and control it with the cylinder stat and control the boiler and pump with the switch actuated by the valve? Do the valves require a constant feed of voltage to stay open, then have a spring return to off once you remove the volts when the cylinder stat opens. Not sure how to control boiler (Myson Velaire) but assume you just give it a 240 volt feed and it actuates the firing process. Is it really this simple ? Nigel P Cat

[Michael Chare]

I am not sure why you have two pumps, but it may be a perfectly viable system, possibly has the advantage of no motorised valves which can be troublesome.

Have a look at Honeywell S Plan

Most motorised valves are spring return, there are very few fully motorised valves.

Quite likely the boiler justs needs power (when there is a demand for heat) and will run as long as it has not reached the upper temperature limit typically set by the temperature knob.

These days you can likely download a manual for the boiler from the Myson web site.

[Dave Liquorice]

Ish. The two pumps complicate things as you don't want to run the CH pump unless there is demand from the CH and vice versa for the HW. But you do need to run either, or both, pumps and the boiler at the same. One if not two relays are required.

Ordinary two port valves yes.

It would be if you only had one pump. B-)

[Roger Mills]

If you've got two pumps, I don't understand why you also want a motorised valve. If you control the HW pump with the cylinder stat, the system will stop heating the water once the stat has turned off. Similarly, control the CH pump with a room stat.

You then need some simple relay logic to turn the boiler on whenever either pump is running.