Identifing CH plan type

[Steve]

I've looked on both the honeywell site and others to try and identify the CH plan used in my house, but cannot find any plan similar to describe what I have.

Basically its an open vented system with the boiler in the garage with one pipe loop through it, and a pump above the boiler connected through a frost stat. The timer is set gravity fed.

The Piping next to the tank is shown here:

pipe is hidden behind the A pipe, which has been redrawn to the right.

Every diagram I see uses a T joint valve, but this has a in line value. There appears to be no other pump in the system.

Anyone seen any diagrams/explanation of this setup? I'm wanting to make a few changes, starting with adding a tank stat, and would like to get some knowledge of the current setup first.

Steve

[Roger Mills]

I don't think that it exactly conforms to *any* of the standard plans!

I assume that the grey box with a wire coming out of the top is a zone valve which, when open, causes the CH to operate?

So when you select HW at the programmer, you'll get the boiler plus the pump running. When you select CH, you'll also get the zone valve opening.

The reason it's set to 'gravity' is that - just as with gravity HW systems - you can't have CH without also having HW. Without this setting, if you were to select *just* CH, the valve would open but the boiler and pump wouldn't run - so you'd get no heating.

It shouldn't be beyond the wit of man to convert it into either a Y-Plan or S-Plan system. For S-Plan, you'd need another zone valve in the pipe going to the top of the HW coil (and you may need to replace the existing one if that doesn't have volt-free contacts which close when the valve is open, and are required for S-Plan). For Y-Plan, you'd need to get rid of the existing zone valve, and put a 3-port mid-position valve in place of the tee piece at the CH take-off point (plus a bit of re-jigging of the pipework). In either case, you'd need a cylinder stat - and a room stat if you haven't already got one.

You'd also need - in either case - to check the connections to the F&E tank - ensuring that the vent pipe always has a clear path to the boiler, with no zone valves in the way.

I presume you've seen the standard plan schematics at

?

[Steve]

Correct.

I'm not sure where ther return is from the CH, or why the water takes the path to the CH instead of the tank when the valve is open.

Interesting, thanks.

yes those were the ones I was looking at.

Steve

[Roger Mills]

With the valve open, the water from the boiler will go to the CH *in addition* to the tank, not *instead* of it. This means that the HW will continue to get hot when the CH is running - until it approaches boiler temperature. This means, in turn, that you either have *very* hot HW (80degC) or you have you use the boiler stat to limit the temperature to about 60degC - so the radiators are not as hot as they should be.

With a proper control plan, you can run the boiler at 80 degC but still prevent the HW from going above 60degC by the use of a tank stat and motorised valve.