Airlock or pump sucking in air?

[nigel.horne]

Hi all

Is there a way to tell if a pump is sucking in air through a union valve? To explain.

I fitted a new central heating pump. I had trouble getting one of the gate valves off so I had to drain down and replace. The gate valve wasn't very snug so I wrapped some PFE tape round the olive and thread. It didn't leak when I put the water back on.

However, since refilling the system the radiator upstairs fills with air almost instantly. I can hear the air rushing in the pump and when I hold my hand on the pipe going into the pump it cools slightly when the air comes.

The vent pipe isn't spitting out any water into the F&E tank. When I put a bag on it it "breathes" sucks air in and then pushes out too.

I've tried refilling the system rad by rad but I have the same problem.

I don't want to take the pump off again if I can help it as it is in a really difficult place, but I feel like I'm not having any success trying to bleed the system.

Any tips for diagnosis would be much appreciated.

Many Thanks

 

[Millsy 82]

Sometimes when you drain a system it can take a while to get all the air out of it (I've had some takes a couple of weeks to get the air out of it)

How quickly did the system re-fill? You may have a partially blocked cold feed that wouldn't show up with an old pump if it has got weaker over time. How is the pipe work in the airing cupboard? A picture would be good.