"Set Square" wrote in message ...
In an earlier contribution to this discussion,
Neal Harwood wrote:

I have a Potterton Profile 50e boiler, and lately the (thermal?)
cut-out has started tripping. This results in the pump going
continuously, but no hot water.
It happily resets manually, and starts up again.
It seems to trip 4/5 times a week, at different times/conditions - no
obvious pattern.

Any ideas?

Obviously I am not going to take the boiler apart (unqualified), but
if the cause is elsewhere in the system, I beleive I could fix it.

Neal

This normally happens when the boiler and pump are turned off by a room
stat - and the residual heat in the boiler's heat exchanger continues to
heat the water to the point where the overheat stat trips.

Boilers which are susceptible to this usually control the pump directly -
and have an over-run stat which continues to run the pump for a while after
the boiler stops firing - in order to dissipate the residual heat.

Clearly, the water must have an available circulation path during this
over-run period - often requiring a by-pass loop, depending on the exact
setup.

The first thing to check is whether your boiler has a pump over-run stat
and, if so, to make sure that it is wired up correctly.

If you still have problems, come back with further details of your system
setup. Does it look like one of the "plans" described in
http://content.honeywell.com/uk/homes/systems.htm ?

Having just read some old (c1998) posts (I Love GOOGLE Groups),
someone else suggested problems with an airlock in the CH system
We HAVE had to drain the system a couple of times over the last year
(to move some pipes and rads in the basement).
Is it possible I have an airlock of some sort? Where would it be?
Would it cause my symptoms? And of course, HOW do I get rid of it?