Central heating peculiar 3 port valve

I would guess that the system is designed to run the pump, and boiler, when the rest of the CH system is otherwise turned off, such as during the night hours. The relay will bypass all of the other controls, so I would expect there to be a room thermostat, somewhere upstairs, to limit the temperature.

Indeed. I had to install one in my central heating.

The problem is in my case was an auxiliary UFH pump. That didn't need to come on when the boiler came on to heat upstairs.

So the UFH timer and thermostat controlled the UFH motorised valve which drove the UFH pump and a RELAY to switch the boiler on.

But if the upstairs or the DHW called for heat it *didn't* switch the UFH pump on.

In practice it forms a sort of electromechanical OR gate. So upstairs OR downstairs can call for heat, but the one wont cause the other to operate

The problem is that the motorised valve only has one set of contacts, the relay adds a second set. So the auxiliary pump is not energised by the call for heat signal

Did you find a valve with the relay, or add it yourself?

My other issue is the plastic cover has broken off teh relay leaving live contacts sticking out of the bottom of the valve

Hi,

I'm not sure it's that clever. There is no room thermostat anywhere on the system and I was always under the impression that rather than it being a true zone it simply either isolated or allowed the upstairs heating whenever the main timer was selected to heating.

Just had another play and it seems that if only hot water is selected (or if the tank stat isn't satisfied) then the relay is not needed, it only comes into play when it is heating, and the hot water is satisfied (ie all flow to the heating circuit)

Looks like the relay is 110V coil which doesn't seem quite right either

There would be no need for the relay, in that case.

Ouch.

Relays are not especially expensive if the cover is part of the relay

The moment you have a separate zone with its own pump you need a relay

Are you sure that's a relay (with a coil) or just a set of contacts?

Common practice on S-plan is that the pump is wired through the valve(s) contacts, so that the valve opens and the contacts registering the open position energise the pump. That sequencing means the pump doesn't try pumping through a partially opened valve, only when the valve has confirmed it is in the open position. It also means that if the valve or its contacts fail the pump doesn't run.

That sounds like the expected behaviour for S-plan. I'm not sure how it applies to a 3 position valve, but perhaps the contacts are break-before-make while the valve is moving. ie if the valve is in position A, contact A is energised. If in position B, contact B is energised. While moving between A and B neither contact is energised. That would cause the pump to turn off while it's switching between heating and hot water.

in other words, like the S-plan wiring diagram but a set of changeover contacts in a single valve, wired so that either contact being made energises the pump.

Theo

So it turns out it is a Honeywell V4073A 1005 which although very old now and unobtainable is the model I have and did have a relay mounted in the valve body.

I found this on another group

Extracted from old honeywell guide. Issue 10 Replacment wiring guide for the old V4073A1005 to all new V4073A models. The old valve had 6 wires and a relay plugged into one end. When replacing this old model with the newer model, wire the new valve colour for colour apart from the brown wire which is missing from the new valve. ON SINGLE OUTPUT TIME SWITCHES Omit brown wire and reverse C & 1 on the cylinder thermostat. ON DOUBLE OUTPUT TIME SWITCHES ie separate switching outputs for heating and hot water circuits.Omit brown wire and reverse C & 1 on the cylinder thermostat.

So I think maybe a tech refresh is on the cards, maybe replace the valve head with a modern equivalent and rewire the whole lot to a standard Y plan and remove the not used 'Zone' valve (might just set it to open or go the whole hog and physically remove it)

Thanks for all the input folks Gordon