Repeated airlocks in central heating system

[gaj2002]

Hi, I had some work done to our house recently, we added some lovely new cast iron radiators, we have eighteen radiators in total now.

The work included a loft conversion with two radiators (one for the bedroom, one for the tiny bathroom). We keep losing heat to these two loft radiators and one particular one on the first floor. We switched from a combi system to an Ideal Logic Max System S30 and a ProLite Air 300litre hot water cylinder.

The remedy seems easy enough, turn off downstairs radiators and force hot water through to clear the airlocks (or gaslocks) or whatever they are. Air/gas is forced into the radiators, whence it can be bled off at a later date. Most of the water has been clear but some has been black/dirty looking.

My problem is that I have had to do this a good few times, it feels like there is a problem beyond the air which would have been introduced from the building works.

The downstairs radiators seem fine, however when I turn them off and then go round turning on the upstairs ones, most of the upstairs ones exhibit a funny gurgling noise (even the ones which had been working). So I guess that is the air moving round.

I tried one time to catch the air/gas bled off in an upturned glass and hold a match to it; nothing happened. But then I'm not very practical so I may have made a mess of that.

Based on googling / looking at these forums, I'm thinking we might need some more inhibitor, I've seen deaerator valves and also magnaclean valves. Also a friend of mine suggested waiting until the radiators are absolutely stone cold to make sure I'm not inadvertently adding more air when I'm bleeding them.

I don't think I'm losing pressure ordinarily so hopefully there is no leak.

Any ideas / advice from anyone here? I would be very grateful

Thanks

 

[terryplumb]

How often do you bleed radiators ?
How many give out air ,and for how long before water comes out ?
What makes you think you have ,or are getting, an air lock ?

 

[gaj2002]

How often do you bleed radiators ?
How many give out air ,and for how long before water comes out ?
What makes you think you have ,or are getting, an air lock ?

Hi, I end up bleeding the radiators about every two weeks, in response to the problem of losing heat at one/two/three of the rads I mentioned above.

Maybe on a typical cycle about five will have air, it varies between a short blast of air being bled out or a more protracted process with a lot of air/water mix having to come out.

I think there are airlocks because I can get scalding heat at all but one/two/three rads, which would be stone cold. Then by turning off all downstairs rads I can get these rads hot (so I presume I’ve moved the air on) and after that there will generally be some air to be bled off where there might not have been before, then I get good performance from my system but typically the problem recurs within two weeks.

So I think I can force through airlocks but I’m worried they keep coming back, the builders said there would be quite a lot of air and it would take a few goes but this seems ridiculous, I’m wondering if there is some reason why this would keep happening.

The builders are good and will come back but I want to be fully armed with knowledge and exhausted everything I can check myself.

Thanks

 

[terryplumb]

Does every rad heat fully at some point ,and days later the upper ones don't heat at all ?
And once bled heat fully ?
Is that the situation ?

 

[gaj2002]

Does every rad heat fully at some point ,and days later the upper ones don't heat at all ?
And once bled heat fully ?
Is that the situation ?

Pretty much, yes.

It’s more than a few days, probably about ten days.

It’s not all the upstairs rads affected, just a few and it varies which ones

And I don’t think bleeding is enough, I need to force the air out of the pipes with the whole turning off of downstairs rads and running the system, then bleed off the resulting moved air, and then I’m ok and everything works

Thanks for taking an interest, look forward to hearing your thoughts

Thanks
Gavin

 

[terryplumb]

I assume the central heating is a sealed / pressurised system and you are continually adding water / topping up pressure ?

 

[gaj2002]

I assume the central heating is a sealed / pressurised system and you are continually adding water / topping up pressure ?

It is sealed and pressurised. I top up the pressure after bleeding, if it needs it, otherwise I haven’t really had to. That’s what is baffling, if there are any leaks then maybe they’re really slow and I get to a bleeding cycle before I find I need to top up the pressure.

 

[terryplumb]

From what you have told me ,it seems that your system is either sucking in air ,or its gassing up.
Was chemical flushing or power flushing done before new boiler etc were installed ?
Is magnetic filter collecting sludge ?

 

[gaj2002]

From what you have told me ,it seems that your system is either sucking in air ,or its gassing up.
Was chemical flushing or power flushing done before new boiler etc were installed ?
Is magnetic filter collecting sludge ?

I thought it wasn’t gas because I tried to ignite it once but to be honest I can’t say in certainty I would have done that correctly.

Not sure on the flushing, definitely not a power flush as I think that would have involved removing the radiators. Chemical flushing maybe, I’ll have to check, probably not. What are the consequences if this was not done?

I don’t think we have a magnetic filter - and yes as I mentioned initially some of the bled water looks a bit dirty. How would that cause these problems? I’m guessing we can still fit one now

 

[terryplumb]

The system should have been cleansed ,and a magnetic filter fitted prior to new boiler install.
One, to prevent system crud Getting into your new boiler ,and two to maximise the efficiency of the system by cleaning out any crud. The filter catching any remnants.

 

[gaj2002]

The system should have been cleansed ,and a magnetic filter fitted prior to new boiler install.
One, to prevent system crud Getting into your new boiler ,and two to maximise the efficiency of the system by cleaning out any crud. The filter catching any remnants.

Ok great, I can check what was done, although if Ideal require a chemical flush then I reckon they would have done that to comply with the warranty conditions.

I’m sure I can get a magnetic filter fitted, perhaps by other engineers. But would that be causing this problem? I’m sure you’re right it needs to be done though.

Perhaps a bit of a random suggestion but the utility room rad has the TRV on the wrong side (return rather than flow). It seems to be slow to warm up so it might be the case that it’s not bi-directional. It’s a Boss TRV from presumably 2007 as that is when the previous owner did their works. Could that be sucking air in and causing the problem?

Thanks
Gavin

 

[terryplumb]

Corrosion in your system MAY be the cause of the persistent problem with gas build up ,if indeed that's what it is. If the system is sucking in air ,it won't have anything to do with a TRV, (which should have arrows raised embossed on its body to show direction / bidirection)
The omission of a magnetic filter ,which I find hard to believe has not been fitted, would not in itself cause your issues ,but may be a contributing factor.

 

[Gasguru]

Has the system got an additional expansion vessel (red coloured) as the boilers vessel will be undersized to cope with the no. of rads and the higher volume of cast iron rads.
If there's no additional vessel you should check the boiler safety valve for drips and if this is the case it could be a source of air ingress.

 

[Gary_Funwick]

If you have eighteen cast iron radiators I suspect the water volume is very high. You need lots of inhibitor. We have steel column radiators and have a similar situation. We had seven (big ones) removed for decorating. When they were refitted and the system refilled we were getting gas in the system that would come back after a few days after being bled. Its taken about 3.5 litres of MC1 to restore everything back to normal. A magnetic filter is a great way to dose the system with inhibitor as well as its other benefits.

Also gasguru is correct - the water volume needs a bigger expansion vessel.

 

[wedge69]

Isn't there just a simple explanation that with such a large system that was completely emptied it's just going to take a while to get all the air out?