A couple of days ago we accidentally (don't ask) drained some of the
water out of the Central Heating system. It's a sealed, fully-pumped,
system: Potterton Prima 80E conventional boiler, Grundfos Selectric
pump.

I've refilled the system and reset the overheat thermostat on the
boiler, which had popped out, and it's now generating hot water again.
However there are various noises, particularly ticking noises from the
pump, wich weren't there before.

Also the boiler casing feels very hot (which worries me) even when the
burner is not going, and the pump seems to be running continously.
Presumably these two are related: the pump is running on over-run and
the boiler is never getting cool enough for the pump to stop.

Now these noises to me suggest air in the system. I know that the
usual solution to air in the system is to bleed the radiators.
However the ambient temperature has been around 30C lately so we
haven't had any radiators on for at least two months. And the
radiators *weren't* drained when part of the system was: we tried
bleeding them before refilling (possibly not such a good idea in
retrospect) and there was water in all of them.

I will try, with some trepidation, to undo the big screw on the pump
and bleed that. But are there any other points which I can or should
bleed to get air out of the system. Or should I try to get water into
the radiators by turning on the heating, as well as the hot water, and
putting the thermostat on its highest setting? (I really don't want
to do this in this weather, but would that be a way of forcing the air
bubble into a radiator?)

Also is there a danger that the pump, or some other component, has
been damaged by running the system dry? The overheat stat clearly did
its job in protecting the boiler, but when the water came out of the
system there were some extremely suspect noises coming from the pump
and elsewhere.

Sorry if the answers are all obvious to the heating experts here. The
FAQ and past posts have been very useful in getting this far.

Martin

"Martin Rich" wrote in message
news
A couple of days ago we accidentally (don't ask) drained some of the
water out of the Central Heating system. It's a sealed, fully-pumped,
system: Potterton Prima 80E conventional boiler, Grundfos Selectric
pump.

I've refilled the system and reset the overheat thermostat on the
boiler, which had popped out, and it's now generating hot water again.
However there are various noises, particularly ticking noises from the
pump, wich weren't there before.

Also the boiler casing feels very hot (which worries me) even when the
burner is not going, and the pump seems to be running continously.
Presumably these two are related: the pump is running on over-run and
the boiler is never getting cool enough for the pump to stop.

Now these noises to me suggest air in the system. I know that the
usual solution to air in the system is to bleed the radiators.
However the ambient temperature has been around 30C lately so we
haven't had any radiators on for at least two months. And the
radiators *weren't* drained when part of the system was: we tried
bleeding them before refilling (possibly not such a good idea in
retrospect) and there was water in all of them.

I will try, with some trepidation, to undo the big screw on the pump
and bleed that. But are there any other points which I can or should
bleed to get air out of the system. Or should I try to get water into
the radiators by turning on the heating, as well as the hot water, and
putting the thermostat on its highest setting? (I really don't want
to do this in this weather, but would that be a way of forcing the air
bubble into a radiator?)

Also is there a danger that the pump, or some other component, has
been damaged by running the system dry? The overheat stat clearly did
its job in protecting the boiler, but when the water came out of the
system there were some extremely suspect noises coming from the pump
and elsewhere.

Sorry if the answers are all obvious to the heating experts here. The
FAQ and past posts have been very useful in getting this far.

Martin
I might consider the air vent valve that may be on the top left side of the
unit. If it will not vent (Presumed to be an automatic vent) the air pocket
at the boiler then the unit will overheat. You can bleed rads forever but
you will find the air pocket at the "HIGHEST" point in any fluid system.
Good Luck