Central heating peculiar 3 port valve

[Gordy]

Hi all,

I was poking around in the airing cupboard weighing up how hard it's
going to be when I have to change the pump and noticed something I have
never come across before.

The system is a Y plan with an extra timer and zone valve (so that when
the heating is on Upstairs is either on or off depending on the extra
timer). I guess the idea is that you only want to heat downstairs in the
day.

Anyway I noticed that the motorised 3 port valve has some kind of
auxiliary relay plugged into the bottom of it (the same side as the
override lever)

I wondered if this was something to do with the zone valve so as an
experiment unplugged the relay. With the relay unplugged the pump
doesn't start, observing it when relay is plugged in it seems to be the
relay energising that starts the pump.

I will do a bit more digging and try and understand the wiring (maybe do
away with he zone valve as it doesn't actually work, I think the valve
is probably stuck open) and maybe return the wiring to classic Y plan.

Has anybody ever seen a motorised valve with an auxiliary relay, no
amount of googling finds one??

Gordon

[Harry Bloomfield Esq]

Post by Gordy
I wondered if this was something to do with the zone valve so as an
experiment unplugged the relay. With the relay unplugged the pump
doesn't start, observing it when relay is plugged in it seems to be the
relay energising that starts the pump.
I will do a bit more digging and try and understand the wiring (maybe do
away with he zone valve as it doesn't actually work, I think the valve
is probably stuck open) and maybe return the wiring to classic Y plan.

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.

[Gordy]

Post by Harry Bloomfield Esq

Post by Gordy
I wondered if this was something to do with the zone valve so as an
experiment unplugged the relay. With the relay unplugged the pump
doesn't start, observing it when relay is plugged in it seems to be
the relay energising that starts the pump.
I will do a bit more digging and try and understand the wiring (maybe
do away with he zone valve as it doesn't actually work, I think the
valve is probably stuck open) and maybe return the wiring to classic Y
plan.

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.

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.

[Harry Bloomfield Esq]

Post by Gordy
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.

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

[The Natural Philosopher]

Post by Gordy

Post by Harry Bloomfield Esq

Post by Gordy
I wondered if this was something to do with the zone valve so as an
experiment unplugged the relay. With the relay unplugged the pump
doesn't start, observing it when relay is plugged in it seems to be
the relay energising that starts the pump.
I will do a bit more digging and try and understand the wiring (maybe
do away with he zone valve as it doesn't actually work, I think the
valve is probably stuck open) and maybe return the wiring to classic
Y plan.

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.

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.

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

[The Natural Philosopher]

Post by Gordy
Has anybody ever seen a motorised valve with an auxiliary relay, no
amount of googling finds one??

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

Post by Gordy
Gordon

[Gordy]

Post by The Natural Philosopher

Post by Gordy
Has anybody ever seen a motorised valve with an auxiliary relay, no
amount of googling finds one??

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

Post by Gordy
Gordon

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

[The Natural Philosopher]

Post by Gordy

Post by The Natural Philosopher

Post by Gordy
Has anybody ever seen a motorised valve with an auxiliary relay, no
amount of googling finds one??

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

Post by Gordy
Gordon

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

Ouch.

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

[Gordy]

Post by Gordy
Hi all,
I was poking around in the airing cupboard weighing up how hard it's
going to be when I have to change the pump and noticed something I have
never come across before.
The system is a Y plan with an extra timer and zone valve (so that when
the heating is on Upstairs is either on or off depending on the extra
timer). I guess the idea is that you only want to heat downstairs in the
day.
Anyway I noticed that the motorised 3 port valve has some kind of
auxiliary relay plugged into the bottom of it (the same side as the
override lever)
I wondered if this was something to do with the zone valve so as an
experiment unplugged the relay. With the relay unplugged the pump
doesn't start, observing it when relay is plugged in it seems to be the
relay energising that starts the pump.
I will do a bit more digging and try and understand the wiring (maybe do
away with he zone valve as it doesn't actually work, I think the valve
is probably stuck open) and maybe return the wiring to classic Y plan.
Has anybody ever seen a motorised valve with an auxiliary relay, no
amount of googling finds one??
Gordon

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

[Theo]

Post by Gordy
Anyway I noticed that the motorised 3 port valve has some kind of
auxiliary relay plugged into the bottom of it (the same side as the
override lever)

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.

http://wiki.diyfaq.org.uk/index.php/Central_Heating_Controls_and_Zoning#CH_and_DHW_zones:_S-plan
has the wiring diagram.

Post by Gordy
I wondered if this was something to do with the zone valve so as an
experiment unplugged the relay. With the relay unplugged the pump
doesn't start, observing it when relay is plugged in it seems to be the
relay energising that starts the pump.

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