Why are my rads getting airlocked repeatedly?

Pique

This has been an ongoing problem for a few years but it's done my head in and I need to get some advice.

I have a back boiler open fire with an OFCH boiler. HW cylinder is upstairs. Vented system with CW tank in attic and expansion tank etc.
Without fail, I have to bleed 3 upstairs rads every month at least and they are almost completely airlocked/cold. One rad downstairs is another regular culprit but less egregious in that it might be every 6 weeks requiring a bleed.

This happens more when a fire is lit so maybe the extra heat from the fire is causing more air to be dissolved(?) from the water?

Thing is, I have never experienced this in any other house I lived in, so is there a simple explanation or more importantly is there any way to solve it? I saw mention of automatic bleed valves for water systems. Can one be retrofitted and would it help?

John.G

Its more than likely that the vent(s) is drawing air in to your system. Go up to the attic and see how many vents you have over the feed and expansion tank, then with back boiler on get a glass (plastic) of water and hold it under the appropriate vent and see if the water is drawn out of the glass, do likewise with your OFCH. Also try and see where the cold feed from the feed&expansion tank joins the system. Also sometime see where both circ pumps are on the flow or return to their respective boilers and check the pump settings.

Pique

John.G wrote: »

Its more than likely that the vent(s) is drawing air in to your system. Go up to the attic and see how many vents you have over the feed and expansion tank, then with back boiler on get a glass (plastic) of water and hold it under the appropriate vent and see if the water is drawn out of the glass, do likewise with your OFCH. Also try and see where the cold feed from the feed&expansion tank joins the system. Also sometime see where both circ pumps are on the flow or return to their respective boilers and check the pump settings.

Ok thanks I'll check the vented pipes and see if there's intake there.

If there is, can I fit one way valves to those pipes? And if so, what kind?

John.G

Should have said which ever system is in use check both vents for air ingress.

No, you cannot fit any type of valve or restriction whatsoever in the vent(s)

Calahonda52

When you bleed the rads, do you have to open the top up loop or is it automatic?

If you have to open it, then you could have a leak or else the system is dumping water into expansion tank, maybe the back boiler is running very hot, or the Circ. pump is set too high

Pique

Calahonda52 wrote: »

When you bleed the rads, do you have to open the top up loop or is it automatic?

No I just bleed the rads and they heat up again.

(I don't know what a top-up loop is)

John.G

You have no top up loop as a vented system, the feed&expansion tank has a pipe from its bottom feeding the system and making up any losses for venting etc, this in turn is topped up by its mains fed ball cock.

Pique

John.G wrote: »

You have no top up loop as a vented system, the feed&expansion tank has a pipe from its bottom feeding the system and making up any losses for venting etc, this in turn is topped up by its mains fed ball cock.

Right, gotcha.

If air IS being drawn in through those pipes, what is the fix? (or is that like asking how long is a piece of string?)

John.G

Could be any number of things......cold feed wrongly positioned or sludge where it joins system......circ pumps speed too high or wrongly positioned......, its further complicated by having two combined systems but depending on what info you can supply it should be fixable, you may have to get somebody in who is familiar with these combined systems.

You can maybe give us some/all of info below.

1. Pump(s) make/model mode and speed setting.
2. Location of cold feed.
3. Vents location
2. Does hot water cylinder have two separate heating coils.

A few photos would also help.