Bleeding pump and freezing rads

[Santorium]

Hi all,

System is gravity fed with a pump for the CH. Pump was replaced in February this year (Grundfos).

At the moment, most of the radiators (I have 5) are begining to get warm but after about 15 mins I get a squealling noise from the pump (turn of and on again to re-set) and radiators stop getting hot.

Have removed the bleed screw on the front and checked the impellor, it does turn.

So I'm thinking that I've maybe got an air lock that's getting sucked into the pump and making this racket?

Plan for tonight is to beed radiators (with pump off, right?) and also pump.

Question 1 - do I bleed the pump when it's swtiched on or off?

Question 2 - does this plan make any sense, or am I wasting my time?

 

[ricarbo]

Make sure you've got water in the feed and expansion tank. Depending on the configuration of the pipework (the feed pipe connection to the circulating loop is effectively at atmospheric pressure plus the head of standing water above it. If this connects to the outlet side of the pump (it shouldn't), the rest of your system will be at less than atmospheric and will draw air in when you open the bleed valves. If the connection is to the inlet side of the pump (conventionally it will be), then the pump increases the pressure in the whole system, so water comes out if the bleed valves are opened). For this reason, it is usually best to bleed the rads with the pump off as the whole system will then clearly be under positive pressure. Once you've done that, I'd bleed the pump when it's off. It's easy to wreck the pump by running it dry for even a very short time. Water wil dry off the bearings in seconds - much worse than running your car having drained the sump of oil! You're on the right track and not wasting your time.

 

[Santorium]

Thanks! Fingers crossed...