Heating System Puzzle

[Davey]

I went to look at a flat's heating system yesterday, which I had been told was not working properly. It was already known that the wiring was f.....d up. None of this was due to me, but it is up to me to fix it.

It looks like a standard 'C' Plan, but the Zone valve isn't sending back an 'Open' signal, and I don't know if it even rotates. It responds to the Manual actuator, but no switch changes state. The valve would appear to be held open when the boiler is running, as the system heats up. In fact the problem is controlling it, as another part of the mess is that the Room Thermostat has been bypassed and lots of wires joined together to make it all run, all or nothing. This I can improve. But the real puzzle is that the Zone Valve only has four system wires, whereas all the schematics I can find shows that it needs five: Power, Neutral, Hot-to-switch Common, Switch closed, Switch open. The valve appears to be wired as, and probably is, a Sunvic 2-port Spring Return valve, which has the correct wires: Brown, Blue, Orange, Grey, Earth. The valves as described in all the schematics I can find also have a white wire shown.

How is this valve, with no white wire, supposed to be used in a 'C' Plan circuit?

The next time I go there (it is a 150-mile round trip), I will attempt to remove the valve actuator, and see what is happening in there. It is, as is often the case, a real pig to get at. I will also confirm that the Zone Valve is in fact in the DHW pipework, and not in the HTG Pump line, just to be sure.

Any help on the 4-wire valve wiring much appreciated.

And finally, if I have to throw in the towel and get somebody in, is there any requirement to upgrade the system to something more modern, or is repairing an old existing system (1976) no problem?

[tabbypurr]

I think really you need to trace what's going on. Or just rewire it. Repair is allowed, though any paid person will of course try to sell you a complete new system.

NT

[Fredxxx]

A C-plan heating system is as simple as you can go.

I'm presuming you genuinely have a gravity fed HW cyclinder with a cylinder stat and the zone valve you mention.

Are you sure it is a C-plan as you need the 5th wire to turn the pump off when there is only demand for HW.

Of course I could be very wrong.

I suggest you take a meter along, and/or perhaps a new motorised zone valve with contacts that work.

You need to check the wiring ensuring what goes to what and what voltages you have on these 4 wires under various conditions.

[thescullster]

On 15/01/2016 00:27, Davey wrote: snip

I believe that they are obliged to talk you into fitting TRVs on rad valves. Others here will recommend that you convert to a pressurised system, although I kept the open vented system and header tank. For reliability sake when I did mine the solenoid valves, stats and pump were replaced along with the system boiler.

Phil

[Davey]

It is a small flat with only three radiators, and the room doors are never closed, except for the bathroom when somebody is in there. So there is zero need for TRVs! And there is nothing wrong with the boiler, hot water tank, header tanks etc, so all I intend to do is sort out the controls.

[Davey]

I intend to rewire once I know how to, with a four wire zone valve! Everything else I understand and can fix, even a temporary method of getting the room 'stat to turn the pump on and off even with the zone valve not working. I am capable of doing it myself, as long as I know what zone valve wire should go where. It is essential that I find out what the valve is doing, if anything. If the actuator needs replacing, that can be done too. But it's the four wires instead of five from the zone valve that puzzles me. As I mentioned, it is a standard product, but I can't find how to make it function here.

[Davey]

Agreed.

Yes, all those components are there, as well as a pump and a room 'stat. The Programmer, a Randall 3060, acts as the terminal block, although one of the previous bodges included the installation of a couple of flying choccy-block terminals where several of the wires are joined together, to get a system that heats water, but does not control anything like properly. When I said it was f....d, I was not kidding. It's like that Eric Morecambe/Andre Prévin sketch: "I'm playing all the right notes, just not in the right order". All the parts are there, they just aren't connected correctly. But I can't work out how to connect what is there so that it will work.

One thing I need to check next time I go there is that the zone valve is indeed in the correct place for a 'C' Plan, otherwise it must be in the pump pipeline, which would require a rethink. It might work, though, so I will prepare some wiring diagrams for that eventuality. All the photos I took were of wiring, not pipework.

And that's the Big Puzzle. It does indeed need the 5th wire, but 'it ain't there, Ma'. I can't get the boiler to come on (schematically) without also running the pump, without that white wire. It might be that the wrong actuator has been installed (it has apparently been replaced at least once), and I just need the correct one, and a new cable with 5 wires, (plus earth). But then, the cable from the valve goes first to a junction box, and the cable from there to the programmer also has only four wires. I suspect that the system has never run fully as it should have, but being a small flat, at least the room thermostat did, at one time, at least control the room temperature. But not now! A valve schematic that I found there was for a valve that needs power to both open and close, with one signal wire. If that was ever there, I have no idea what the thinking was.

One other question: Reading the instructions for a similar Sunvic valve, it looks as though the flats on the valve stem are at right angles to the direction of the moving valve body port. The assembly instructions say to put the flats parallel to the pipe direction, and then install the actuator, which means that the default position of the stem flat, with the actuator non-powered, is with the pipe, while the valve is actually closed. This matches what I found when I had to sort out the zone valve in my own house. But it is the opposite of industrial practice, which sensibly has the flats parallel to the valve body hole. So the question is: In the world of heating systems, is the valve stem flat at right angles to the flow hole in the rotating valve body? And if so, why? It seems counter-intuitive, to me at least.

All help and useful suggestions welcomed. Thanks for thoughts so far.

[Fredxxx]

Personally I would consider going for a Y-plan, or a fully pumped system with two zone valves, one for CH and the other for HW. It depends on where your pump is, or where you could fit one.

If you have a set of closed contacts on one zone valve you could still keep that. Just wire the closed contacts together to fire up the boiler and pump.

[Chris French]

Well, that's what should already happen for the CH.

It's apparently a C plan gravity feed hw system - basically the zone valve is in the gravity circuit to stop water circulating in the primary HW circuit once the tank stops calling for heat.

As to the last bit of the OP's question, no you can just repair the system , no need for upgrading.

[Davey]

The place is too small to even consider system modifications, and what is there is fine functional, it just needs sorting out.

The problem is that I don't want to run the pump if only DHW is required, although it may be that that is how the system was working before it got bu.....d up (by professionals, I am told!).

[Davey]

If I want DHW only, that isn't right. But it may be a temporary solution, until I get it fixed properly. I already have plans for that drawn up.

It's a small 1st floor flat, and needs very little heat. There is no intention of replacing perfectly good equipment, at great expense.

[Chris French]

In message , Davey writes

When you said at the beginning of your post that the heating system wasn't working, what did that actually mean in terms of symptoms?

You appear to be saying that the system is messed up, with the wiring bodged up so that everything, CH and HW either works or doesn't work together? Is there a programmer, you don't mention that. Can you turn off the CH side of things?

I suspect the answer is that this isn't a proper C plan system, and that the wiring has been bodged up so that it works in some fashion, hence the incorrect 2 port valve wiring. The white wire is normally used just to carry the room stat call for heat signal to the pump microswitch and then back to the boiler. It sounds like someone has been creative to make things 'work' in some fashion.

If it was me I think I would just get a new 2 port valve with the necessary wires, put that in and then rewire it all so that it all works properly.

[tabbypurr]

NT

[Davey]

The main symptom is that there is no response to the Room 'stat switching, then that the DHW output does all the timer controlling, and also that the CH pump runs all the time that this output is 'ON'. Other than those things, it's fine!

I did in fact mention a Programmer in my 17:42 message, it is a Randall

3060, which appears to be fine, as far as I can tell. It is also the terminal strip, which is fine.

I think it is piping-wise a 'C' Plan system, but with the wrong valve actuator, and so electrically bodged to make it sort-of work. The last bodge was a really good one, bypassing the room 'stat completely.

That is my plan. I believe the valve is probably ok, and if so, I will just need a new actuator, and a bit of cabling. I cannot see how it can be properly functional with the present actuator, nor that it can ever have been fully correct. Now I just need to get my contortionist's diploma.... The valve is, of course, behind the tank, jammed between it and the wall, and presently almost covered by the tank insulation blanket.

[Davey]

If anybody knows about these actuators, I think I would need a Sunvic SZ2302 Actuator. Valve Normally closed, s.p.d.t switch. Is this the correct unit? I think that the current actuator is probably an SZ2301, non-functioning, or equivalent.

[ARW]

Now the first link to a SZ2302 I found shows it as a 4 wire device with a twist on the C Plan wiring!

It seems that the NO connection of the switch (your missing white wire) is internally connected to the valves motor.

[Fredxxx]

Interesting, it seems the brown is common to eliminate one of the wires. Well found.

[ARW]

I think

would be the new wiring diagram for the SZ2302 (and the white wire is now grey).

Opinions welcome.

[Roger Mills]

Indeed. The internal link between NO and motor feed would do away with the need for the grey (permanently live) wire in the more usual schematic. That should certainly enable the valve to work properly in a C-Plan system without requiring a fifth wire.

[Davey]

Wow! That would mean that the existing valve, if it worked properly, would be suitable, maybe with an internal jumper added. Thanks folks, I'll take a look at that as a possibility. Much appreciated.