Air getting into water system

[bilbobaggins88]

Seems our hot water heating cycle is suffering from ingesting air from somewhere.

Tonight, whilst the hot water cycle was on there was a change in the speed of our WBosch Greenstar condensing boiler, followed by a rushing noise then lots of banging from pipes above. The boiler then switched off.

I turned off hot water and set the boiler to radiator heating and nothing heard, it's run sweet and quiet for a few cycles of the radiator heating. I do wonder whether the heating system is pushing air to the radiators as I can hear at least two gurgling slightly.

How can I start to diagnose where in our system air might be being fed in please?

We have a hot water cylinder, diverter valve, pump, and a header tank in loft. No apparent leaks anywhere.

A plumber has suggested a pressurised system, but I'm worried some of our rads are a little rusty and might burst?

All suggestions welcomed.

Thank you!

 

[bilbobaggins88]

Boiler serviced in October and another plumber visited in January to bleed the system, found lots of air in several rads

 

[Johntheo5]

Seems our hot water heating cycle is suffering from ingesting air from somewhere.

Tonight, whilst the hot water cycle was on there was a change in the speed of our WBosch Greenstar condensing boiler, followed by a rushing noise then lots of banging from pipes above. The boiler then switched off.

I turned off hot water and set the boiler to radiator heating and nothing heard, it's run sweet and quiet for a few cycles of the radiator heating. I do wonder whether the heating system is pushing air to the radiators as I can hear at least two gurgling slightly.

How can I start to diagnose where in our system air might be being fed in please?

We have a hot water cylinder, diverter valve, pump, and a header tank in loft. No apparent leaks anywhere.

A plumber has suggested a pressurised system, but I'm worried some of our rads are a little rusty and might burst?

All suggestions welcomed.

Thank you!

Can you get someone to start the boiler while you watch the vent over the header cistern and see if there's a spurt of water when the pump starts, get the boiler stopped and keep watching the vent until the pump stops maybe 2 or 3 minutes later, pump overrun, again watch for any spurt of water. With the boiler running, hold a "glass" of water with the vent end immersed in it and see does the level fall in the glass.

Before the pump inlet have you got the cold feed nearest to it and no more than 150mm further back towards the boiler, the vent?

How many rads?
What is the pump make/model/mode/setting? If its a A rated pump with LEDs and you are not sure of its mode&setting, post a photo of the pump+LEDs, pump running.
Was the pump renewed recently?

 

[bilbobaggins88]

Thanks John, the Drayton actuator was swapped out Spring 2022, and as heating system was used in anger in the autumn we first noticed air pocket problems. The Grundfos pump with display was swapped out earlier than that.

To me, it seems like air problems occur after limited use of heating or hot water. I turned down central heating for long weekend away, but left hot water system on like normal. To try to save gas money.

I can ask the first plumber available to try your theories thank you. My wife had just filled the bath before the hot water heating last complained, and I do find that hot water pressure to the sink tap drops to little/nothing when this happens. Could the flow to the header tank be too little?

Thanks again

 

[bilbobaggins88]

One plumber told us to turn up speed on pump, another to lower it

 

[bilbobaggins88]

12 rads, we specced the new boiler about six years ago, to cope with this many

 

[dilalio]

Use a magnet around the feed and vent to see if it sticks. Indicating blockages.
Very common place to block.
Also consider combining feed and vent.

If you've been getting air in for a period of time then there will be sludge.

 

[bilbobaggins88]

Thank you, a decent plumber should know these things, is that correct? I could suggest these ideas if they get stumped, but don't want to suggest in advance. I can't get the same plumber each time, so have lost touch with who's done what.

 

[Johntheo5]

Thanks John, the Drayton actuator was swapped out Spring 2022, and as heating system was used in anger in the autumn we first noticed air pocket problems. The Grundfos pump with display was swapped out earlier than that.

To me, it seems like air problems occur after limited use of heating or hot water. I turned down central heating for long weekend away, but left hot water system on like normal. To try to save gas money.

I can ask the first plumber available to try your theories thank you. My wife had just filled the bath before the hot water heating last complained, and I do find that hot water pressure to the sink tap drops to little/nothing when this happens. Could the flow to the header tank be too little?

Thanks again

You can figure out the problem yourself.

OK, take a picture of the running pump ASAP and post it on, if its a grundfos UPS3 running at full speed then you will definitely get air ingress, but once we see a photo we'll get a good feel as to whats going on.

Even if you're as old as me, which is doubtful, you can get up the attic? and get the wife to start/stop the pump and watch for that pump over.

 

[Johntheo5]

One plumber told us to turn up speed on pump, another to lower it

Some open vented systems, except its the perfect one, like mine, with some rads over 40 years old, are very sensitive and its vital to get the pump head just right and certainly not too high.

 

[bilbobaggins88]

The vent thing in airing cupboard is on the way from actuator to bottom of hot water cylinder

 

[bilbobaggins88]

Sorry John, I'm a wimp with this sort of thing and the shallow pitch on our house roof makes me claustrophobic in the loft. I don't mind paying a plumber, so long as they know what they're doing, and sometimes local plumber needs 3 visits to fix a leaking toilet cistern.

 

[bilbobaggins88]

I hear a big bubble of air in what I think is the hot water tank most days hours after the heating has turned off.

 

[Johntheo5]

Thanks, I'll have a look at the pump curves later but 19W indicates that it not running with a unduly high head so this is unlikely to be your problem.
The vent we are talking about is a pipe that goes right up and over the F&E (header) cistern, if you look first at the pipe going into the bottom of the pump and follow it back a bit you might see a biiger (22mm) and smaller (15mm) pipe teeing (joining) into this pipe, if not follow the pipe from the top of the pump (it might be pumping downwards) and ditto, post a photo if you locate them.

 

[Johntheo5]

I hear a big bubble of air in what I think is the hot water tank most days hours after the heating has turned off.

That might be a separate/different problem.