DIY Doctor

[color=red]H/W and Heating constantly ON[/color]

Postby shipoftheline » Sat Jan 03, 2009 2:45 am

Hot water and heating always on.
Thermostat = off (turned to minimum)
Programmer = HW set off, CH set off
CH pump runs almost constantly. Stops appox. every 5 mins for 30 secs then starts again.
Radiators constantly hot as is hot water

Potterton Prima 30B (Loft install)
Water tank (Loft)
Emersion cylinder
Drayton thermostat in hallway
Honeywell ST9400C Programmer
Honeywell motorised valve, type unknown, is a T shape, connects to emersion cylinder with the 2 other connections going elsewhere

In the last 2 weeks, the h/w and heating has remained on regardless of settings. In terms of the heating, turning the themostat to zero does not switch it off, nor does turning off the heating at the programmer. Turning off the h/w at the programmer also makes no difference to the h/w.
The CH pump runs almost constantly. Stops appox. every 10 mins for 30 secs then starts again.
The boiler fires up every 2/3 mins or so for a very short period as if the thermostat is on max.
The thermostat was replaced 1 yr ago
I changed the programmer last week as the original had seen better days but the problem didn't go away.

Any advice/experience gratefully recieved

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Simply Build It

Postby plumbbob » Sat Jan 03, 2009 4:12 pm

Have you checked to see if a frost stat is connected. As the boiler is in the loft, it suggests you should have one. If it is set too high, (or the air temp is below 3 degrees) then this stat will override all other controls and produce the symptoms you describe.
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