Multi Zone heating problem

[Mark kennerley]

I have just had an extension completed with a separate UFH zone added meaning i have 1 zone for the radiators in the house and 2nd zone for the UFH.
Unfortunately it seems that when the UFH comes on it also turns the house radiators on too and they are uncontrollable meaning the house becomes a complete sweat box. I have had a 1 month period where it seemed to work all ok but then i bled 2 radiators and the problem has come back.
The plumber who installed the UFH has said that he thinks the return is in the wrong place. He has said ideally it should be behind the HW return but it is not there.
There seems to be no problem when the HW comes on and the 3 way port has recently been replaced.
I am hoping someone maybe able to offer either confirmation of what i am being told or another explanation, i am no longer certain that the original installation of the UFH has been completed correctly. Thanks very much.

 

[Mark kennerley]

What is the default resting position of the 3 port? It seems that when call for heating comes to the 3 port nothing happens but when HW is called for the port moves. Is this the wrong way round?

 

[Ric2013]

_Normally_ motors quietly to the heating position, with a noisy whee- pa! spring return noise to the hot water position.

 

[doitmyself]

What is the default resting position of the 3 port? It seems that when call for heating comes to the 3 port nothing happens but when HW is called for the port moves. Is this the wrong way round?

The ports of a mid-position valve are labelled: AB, A, and B. AB is the inlet, A the outlet to radiators, and B the outlet to HW cylinder.

When the valve has no power to it, it will be at rest with port B open. The status of the valve when powered depends on which wires are live and the sequence in which they are turned off.

White live: valve in mid-position (A & B open): CH and HW both on
White and grey both live: A only open: CH only on.

If CH is then satisfied, power is removed from the white but grey remains powered. This means the valve remains with port A open, so the rads will get heated, uncontrolled, as you have found out.

There are two ways of removing power from the grey wire: turn power off at the main switch, or a call for heat from the HW cylinder. As the first is not practical and the second cannot be guaranteed, the only solution is to replace the mid-position valve with two zone valves.

 

[Mark kennerley]

The ports of a mid-position valve are labelled: AB, A, and B. AB is the inlet, A the outlet to radiators, and B the outlet to HW cylinder.

When the valve has no power to it, it will be at rest with port B open. The status of the valve when powered depends on which wires are live and the sequence in which they are turned off.

White live: valve in mid-position (A & B open): CH and HW both on
White and grey both live: A only open: CH only on.

If CH is then satisfied, power is removed from the white but grey remains powered. This means the valve remains with port A open, so the rads will get heated, uncontrolled, as you have found out.

There are two ways of removing power from the grey wire: turn power off at the main switch, or a call for heat from the HW cylinder. As the first is not practical and the second cannot be guaranteed, the only solution is to replace the mid-position valve with two zone valves.

Brilliant explanation thank you, thought this would be the case but did not know why.