Motorised valve performs erractically

Desperatedan · Feb 6, 2011

I have a pumped gas central heating system. I recently had to replace the mv (honeywell) with a sunvic 3 port , 3 position valve (CH,WH,Mid position). I was told that this should work ok.
The problem I have is that the actuator will not respond to HW stat call when the room stat is SATISFIED - other than this the mv works fine, however it does not seem to be able to stop in mid position; the system did not do this previously.
The controls are linked through a Drayton RB2 control box.The system is time controlled ; separate instructions for HW only or Room heating are not present. Previously the system gave priority to WH over RH.
The connections to the RB2 are as follows-
Terminal 1 (A)......mv(grey), cyl stat (satisfied)
2(A)......room stat ,I think
3(B)......cyl stat (common)
4(B........live feed (2 red wires)
5(1)......pump (blue)
6(1)......mv (blue)
7(2)......cyl stat (demand)
8(3)......room stat (demand)..I think
9(4)......mv (orange)
10(5).....mv (white)
11 (6).....pump (orange)

All wire connections are as previously with only the wires from the new mv being connected in a similar arrangement as the earlier mv ie. similar colours to same terminals .
I hope that someone might be able to advise how I can correct this situation.

tamz · Feb 6, 2011

An RB2 is a relay box that was used with a flowshare system. The original valve would have been a Drayton TA/M4.

Your need to remove the RB2 and wire it as a Y plan.

Desperatedan · Feb 6, 2011

Hi Tamz,
Thanks for reply. I had a feeling that the new mv would probably be incompatable with the existing system unfortunately I have been unable so far to get details of how the rb2 works.
presumably if I rewire the units through a terminal block directly then I can dispense with the relay.
I already have some prints of the y plan wiring so hopefully I should be able to make the system work correctly including having the benefit of the mid port facility.
Your reply much appreciated.

doitmyself · Feb 6, 2011

Desperatedan said:
I recently had to replace the mv (honeywell) with a sunvic 3 port , 3 position valve (CH,WH,Mid position).

The problem I have is that the actuator will not respond to HW stat call when the room stat is SATISFIED - other than this the mv works fine, however it does not seem to be able to stop in mid position; the system did not do this previously.

Previously the system gave priority to WH over RH.

You have bought the wrong valve!

You have a W Plan (HW priority) which uses a diverter valve, not a Y-Plan (mid-position) valve. If you want to you could rewire the system as a Y plan.