3-port mid-position valve / Y-plan question

[MrTom]

Hi there,

I have a Y-plan setup (Ecotec plus 630 boiler, Honeywell timer, roomstat and cylinder stat) heating rads and a hot water cylinder.
I'm 99% certain the valve is wired up correctly and switching properly, but when there is demand for CH and HW, the rads all drop in temperature quite a bit. First thing in the morning in winter, CH & HW will be on for 2 hours but the house will feel quite cold like the heating's barely been on.

I did recently balance the rads as the ones near the top of the house weren't getting hot. Could that affect the way the system behaves when there is demand for CH and HW i.e. water taking the path of least resistance via the HW circuit?
Is there an equivalent 'balancing' exercise I should carry out on the HW circuit to even things out, or is this just the way a Y-plan system behaves?

Thanks in advance...

 

[Dan Robinson]

Is it a 22mm valve?

If so then no wonder. The poor boiler will be dazed and confused at best.


a 630 is pretty meaty, do you reeeeaaallllly need that output?

 

[MrTom]

Thanks for quick reply Dan.

Pretty sure it's 22mm but the panels are all back over the piping now so can't check 100%...

I've set the partial load on the boiler to 18kW as others have advised it's a tad on the large side, will that help?
Anything else you'd recommend?

 

[D_Hailsham]

Is there a gate valve on the return from the cylinder? If so, use it to balance the flow through the cylinder. It then won't grab all the heat.

Also, set the HW to come on an hour before the CH. The cylinder should then be up to temperature before the CH starts.

 

[Dan Robinson]

Certainly stagger the demand. A good hour as you have an old cylinder (just remembered your other thread) maybe more.

As for the balancing valve.... Play with it. I have found that it needs to be fully open to get the flow rate through the boiler to keep the controller happy. Too little flow and the boiler will cycle prematurely and give you precisely the problems you are experiencing.

This is where true separation between hot water and heating controls comes in.

 

[MrTom]

Cheers D_

Pardon my ignorance but what is a gate valve? Just a regular valve? There is a largish round red-handled valve near the cylinder which I *think* is on the return pipe - might that be it?
To balance it, would it be similar to rads?
What sort of temperature drop should I aim for?

Have set HW to come on for an hour before CH for now, but thought that would use more gas in the long run no? i.e. doing two separate jobs for longer rather than a combined job for less time as it were...

 

[Dan Robinson]

kW's are kW's.

If the house and cylinder need them, they will absorb them Running the circuits individually or side by side will not adversely affect the efficiency providing things have been balanced and above all sized adequately.


Yes to your other questions about the gate valve.

Try the system with hot water only and the gate valve open fully (but turned back half a turn). Does the boiler fire for longer before hitting S.53 (or is it S.28? the brain is going fizzy).

 

[MrTom]

Thanks Dan - on the KW's question, I'd have thought a 30kW boiler would be able to adequately heat both circuits at the same time, wouldn't you? It's 11 rads + HW cylinder...

 

[Dan Robinson]

It would probably do both twice over. But it is down to the pipework, valve, boiler heat exchanger and pump being able to disperse the heat in a timely fashion.


Your issue I would wager, is related to this.

 

[MrTom]

Gotcha, cheers