Central heating problem

[paul.wordingham]

Hi,

I started to look at this earlier this year, but then forgot as summer was upon me..

I have a gravity primary hot water system, with pumped central heating via microbore pipes to the radiators. The tank-thermo operates a 2 way valve when the tank reachs temp. However when the valve is shut, it stops the water-circuit for the ch, and although the pump is spinning the rads go cold. If I manually open the valve the rads start warming up. I have checked all the wiring against the honeywell C-Plan system, and everything looks ok, and all the wires go live when expected. So I am now assuming that the valve is in the wrong place or the plumbing is a little non-standard !

I experimented with wiring the live from the room-thermo to the 2-way valve, to open the valve when the room gets cold.. and it works.. but of course if the tank-thermo wire goes live, it can "feedback" to the ch pump. And the rads get hot when the room is already up to temp, it can get a bit warm..!

Does anyone have any bright ideas how I could wire the room-thermo to open the valve, without interfering with the input from the tank-thermo. I think I need some sort of switch with 2 isolated inputs, and an output if either goes live ?

I don't fancy having to replumb the system.. :-) before you ask.

Thanks in advance,

Paul...

[Set Square]

Let's assume to start with that the valve is in the correct place - 'cos it probably is - and doesn't *physically* stop the flow to the radiators.

Are you *sure* that it's wired correctly? The wiring of the secondary switch on the motorised valve - which operates when the valve is fully open - is

*very* important.

You say that when the valve closes, the pump runs but the radiators don't get hot. You don't say whether the boiler fires. Does it?

If not, the wiring is almost certainly wrong. Have a close look at the C-Plan wiring diagram in

orange wire *must* be connected to the boiler. The grey wire *must* be connected to permanent live, and the white wire to the pump *and* to the room stat.

This is a very cunning system which runs just the boiler - and opens the valve - when HW is required, runs the boiler *and* pump when CH is required - and shuts everything down when both demands are satisfied. Furthermore, it does it without needing any relays BUT it only works when it is wired *exactly* as shown in the Honeywell diagram.

[paul.wordingham]

Set Square,

I have been thru the wiring, time and again, and cannot see any problem.. but I am always willing to admit a mistake ;-)

I wil check to see if when the white goes live, that the orange wire goes live as well to fire the boiler. Maybe a issue with the secondary switch ?

Will be back..

Paul...

[Set Square]

Of course, if the boiler *does* fire - but the rads don't get hot - it could indicate that the valve *is* in the wrong place, but that wouldn't be my starting position. How many connections are there to the boiler? Are the HW and CH circuits completely separate, or are any parts common? If there are common parts, where is the valve in relation to these?

[paul.wordingham]

I did some testing last night. and the wiring seems ok. The orange wire from the valve goes live when the room-thermo asks for heat, and feeds the boiler to start it. All the other wiring, seems to be correct as well, and goes live when I expect it to. With the pump spinning, and the valve closed, I can feel the input pipe to the pump feels cool. If I then manually open the valve, the pipe goes hot and the rads warm up..I was hoping that it was something wrong with the wiring, but it is increasingly looking like the valve location.

Any ideas how I can work-around it ?

Thanks,

Paul...

[paul.wordingham]

I did some testing last night. and the wiring seems ok. The orange wire from the valve goes live when the room-thermo asks for heat, and feeds the boiler to start it. All the other wiring, seems to be correct as well, and goes live when I expect it to. With the pump spinning, and the valve closed, I can feel the input pipe to the pump feels cool. If I then manually open the valve, the pipe goes hot and the rads warm up..I was hoping that it was something wrong with the wiring, but it is increasingly looking like the valve location.

Any ideas how I can work-around it ?

Thanks,

Paul...

[Set Square]

Have a look at my previous post which asked about the number of (plumbing) connections to the boiler - and whether any parts of the CH and HW circuits are common - and the whereabouts of the valve. You'll need to provide answers to those questions before we can take it any further.

[paul.wordingham]

It is very difficult to see where the plumbing connections go, as both the ch heating and hw pipes disapear round the back of the hot water cylinder. For the moment I have latched the valve open, and turned the boiler control down to low, to ensure that the water does not get heated too much.. but this is not ideal !

There must be a way of fitting some sort of relay that will output a live when either / or of the hw & ch inputs are live..?

The electrical inputs to the boiler look ok as the orange from the valve feeds the live input to the boiler.

[Set Square]

From your previous posts, it's beginning to look as if the valve is in a bit a pipe which is common to both circuits rather than just being in the HW circuit.

If you do *that*, you'll open the valve whenever the CH is on - even if the HW demand is satisfied - and you'll overheat the HW. This defeats the whole idea of having a valve!

Sorry, but you really need to understand what all your pipes do - even if it means grovelling round the back fo the cylinder with a mirror - so that you can work out where the valve needs to be.