Dreaded air in upstairs radiators and heating is off

[nairb999]

Recently had my boiler replaced and had air in one radiator since replacement. The heating has been off for the summer so decided a few days ago to run the system to make sure TVR's were all good . The boiler was OFF during this test and to my surprise had air in 6 radiators after testing the rads the morning after. Bled the rads and tested again after another day. This time I did not turn the pump on but still managed to get air out of the radiators.

How can this be?

 

[Johntheo5]

Was the system chemically cleaned and flushed out properly afterwards and inhibitor added?.
Is it a sealed or open vented system?.

 

[nairb999]

Thanks for prompt response. It is open vented and inhibitor was added. System drained but not cleaned. Gas engineer who installed the new boiler said the system was very clean after draining

 

[Johntheo5]

The new rad should have been flushed out before installing but often isn't so don't know if this would really cause those "air" problems.
Is it a oil/gas boiler and what kind of vent & cold feed arrangement have you, if the circ pump is external is it installed high up on the system.

 

[nairb999]

Gas boiler
boiler vent feed pump
Boiler downstairs. Vent feed and pump in airing cupboard on 1st floor. Expansion tank 2 meters above in the loft

 

[Johntheo5]

If you havn't had previous air ingress problems then maybe just requires more venting until all the air is expelled from the system.

 

[nairb999]

Thanks for your help

 

[terryplumb]

Do you have a hot water cylinder ,and boiler heats the domestic hot water ?

 

[nairb999]

No hot water system. Separate gas water heater.

 

[Johntheo5]

You havn't said if you had previous problems, what pump/model/mode/setting?, presume its not a new pump that you installed with the new rad?, also check for any pump over through the vent when the pump is starting and also when stopping. The new boiler may have a lower HEX head loss leading to pump over.

 

[terryplumb]

When was the boiler replaced ?
What radiator was replaced ,if any ???

 

[nairb999]

The boiler was replaced in February. It is a Baxi 619 heat only boiler. No radiators replaced. Wilo Stratos Pico 1-6. On start up suction is felt on the feed pipe for a few seconds. No suction on vent pipe. When turn the heating off no action on the feed pipe and a little air comes out of the vent pipe. This boiler is a condensing boiler and has replaced a Potterton Prima F60 which had no air issues. In the 2 months the boiler ran before shutting down for summer did get air in 1 rad in the bathroom highest point.

 

[Johntheo5]

The boiler was replaced in February. It is a Baxi 619 heat only boiler. No radiators replaced. Wilo Stratos Pico 1-6. On start up suction is felt on the feed pipe for a few seconds. No suction on vent pipe. When turn the heating off no action on the feed pipe and a little air comes out of the vent pipe. This boiler is a condensing boiler and has replaced a Potterton Prima F60 which had no air issues. In the 2 months the boiler ran before shutting down for summer did get air in 1 rad in the bathroom highest point.

Its probably the reduced Baxi HEX head loss even though theoretically you should not have any problems with your VCP system ( boiler, Vent, Coldfeed & Pump), there may be a partial blockage where the cold feed is teed into the vent or around that area, but would need cutting out to check it, however the pump may be set to too high a mode& setting (I have one myself) so can you first of all just take a photo of the setting knob position on the pump, then run the pump and it will show the power in watts (W) it may show the flow as well in M3/hr, something like 0.5 to 0.7, post on findings/photo.

 

[nairb999]

Many thanks again for your very useful suggestions. Presently not at home but will be back around mid day. Pump was on 4.0 and PV setting. It shows the power setting but I don't think flow. Was also set on dynamic setting but turned this off.

 

[nairb999]

Another bit of information which could negate potential blockage. Have tried the magnet test on all pipes in that area and no pull detected. I did this test 10 years ago and had several areas to replace