converting gravity fed HW CH to something better

[nospam]

Just when I thought I had figured out what I was doing, I've been looking at the boiler again. The HW side is easy to get at but the CH side is squashed next to a cupboard. To rearrange the plumbing means taking the cupboard out, only the oven is on top!

I'm wondering whether to leave the CH as it is and just add a valve and a second motor in the airing cupboard on the HW.I know it's not ideal using two pumps when I could use only one but it might save dismantling half the kitchen. Do I need a two port valve on the CH to switch that offor is flow minimal when the pump is off?

Thanks.

[Roger Mills]

Suck it and see. If you get too much gravity circulation when the CH is on but the HW pump is off you could insert a check valve rather than a motorised valve. That's just a simple mechanical device which requires pump pressure to open it, and thus prevents gravity flow.

If you go with a two pump solution, you *will* have to sort out the control logic, as I mentioned earlier. You need to control the HW pump with the cylinder stat, and the CH pump with the room stat. You then need some logic which turns the boiler on when either or both pumps are on *without* turning the other pump on if only one is required. You'll have to figure out how to do that!

[The Natural Philosopher]

Why not use one pump and two valves? Or have I missed something? Oh I see..the OP suggeested two..

the control logic here is a pain. You need two relays basically, one wired across each pump and the contacts in parallel so that either pump will cause the boiler to fire, but one pump won't cause the other to operate.

[Roger Mills]

Because he wants to keep both circuits since he can't get to the CH side of the boiler without dismantling his house.

[nospam]

Well, it seems there are no easy answers. If a job's worth doing, it's worth doing properly. I think it would be best if I can take the side off the cupboard and try to get at CH through the side of it. At least if I have a "standard" installation, it won't confuse any plumbers that work on it in the future, or any future resident if I ever move house and it saves the headache of the relays. Thanks for your help.