"Tony Commander" wrote in message
om...
Having just moved into this house I have not fully had time to explore
the central heating system yet, so details might be a little bit
brief..

But hopefully someone may have had this problem before!

Normal (not combi) potterton bolier in the kitchen that looks a good
10-15 years old, with hot water tank upstairs.

Timer is one of the really old fashined ones with the red/blue pins
for on/off on the dial, and thermostat in the living room.

Problem..

Even with thermostat down as far as it will go, radiators remain hot,
only way to cool them down is to turn off the central heating fully.
Have not yet confirmed whether they cool down if we turn c/h off but
leave water on... thats next on my list!

(When you turn the thermostat up you can hear the pump start, but the
rads are hot anyway)

Given that the rads remain hot, even when the pump is not pumping,
could it be a faulty pump valve allowing hot water to circulate via
convection, or is likely to be more serious?

You say the pump is definitely not running when the system's providing hot
water only.

There are no zone valves (motorised valves) in the system?

You will, I expect, have 28mm / 1" pipework between the boiler and the hot
water cylinder.

Therefore (as others have surmised) the hot water is heated by gravity
circulation alone. Maybe there is some partial blockage in the hot water
pipework, encouraging water to circulate around the heating circuit? You
should have a non-return valve in a vertical section of the flow pipework
from the boiler to the HW cylinder - maybe this is partially blocked?

In the short term* you could try turning down the valves on all the
radiators so that they still heat up when they're supposed to i.e. the pump
is running, but discouraging gravity circulation.

* i.e. if it works, indefinitely :-)