Central Heating 'S' verses 'Y' plan

[Gasguru]

Go for a couple of 2 port Honeywells - reliable and easy to repair if there are any problems. Also wiring is considerably easier.

In my experience (as htg eng.) 75% of mid-position systems aren't wired up correctly.

Keep it simple.

 

[chrishutt]

few people can wire them from memory

White to CH on, Grey to HW off, Orange to HW on and boiler/pump. Is that so difficult to remember? (OK, I admit I looked it up before posting )

 

[Agile]

If you are honest, Paul?

Well, I would assume that everyone here IS honest!

Someone says after their signature, "never assume anything!"

Tony

 

[ollski]

Y plan has the potential for one valve to go wrong and an s plan has the potential for 2. I go y plan for a standard installation and s plan for multi-zoning or unvented.

 

[chrishutt]

I've just installed a 3 port valve (Y plan) to control 2 heating zones in association with a combi boiler. Top zone is as if CH side, bottom zone is as if HW side. Anyone think that's not going to work

 

[Paul Barker]

OK Tony what I mean is if I search deeper into my motivations one comes to the surface which I wouldn't at first offer as my rationalle.

Surely two reliable valves are better than one which you read about problems with all over the net, and causes many of the heating call outs we get. OK maybe good for business then, I'll shut up.

 

[ChrisR]

A two port valve and a three port in one of its positions all leave the motor energised and stalled.

NOT correct Tony - think about it a bit more!

If anyone wants to they can use motor-open, motor-closed valves. It might be thought that these would be more reliable. Can't answer that myself, I know I have changed a few MOMC heads, and there are very few out there as a %age.

Saw an ad recently for a valve which was spring return but turned the power off when the valve got to its position, Sunvic I think.

There's no point making the motor last forever, they all leak through the spindles sooner or later!

3 ports are easy to learn the wiring for. All plumbers will have heard of Grey Water, and that leaves White Heat. Water is negative logic, so you need ALL the "Water Off" signals, which includes the one ChrisH left out- coming from the programmer as well as the cylinder stat. Trivial!

 

[chrishutt]

which includes the one ChrisH left out

I didn't leave it out, I just didn't specify it. Anyway if you're using the valve to control two zones (as I've just done) there won't be a cylinder stat off, just the off input from a programmable room stat or equivalent (a seperate room stat wouldn't give you the off input required).

 

[Agile]

A two port valve and a three port in one of its positions all leave the motor energised and stalled.

NOT correct Tony - think about it a bit more!

I have thought again and confirmed that what I previously said was correct.

Of course there are different types of valves about but what I said applies to the standard spring return valves. Everything has to be taken in its context.

Like learning the wiring for a three port valve system, apart from ChrisR only a very few people know it enough to wire it from memory. Even with a diagram many people get it wrong, probably 10% of the system faults I have been to fix have been wrongly wired!

Tony