How to stop excessive air in central heating?

[Pirbrightgolfer]

I have a central heating system and hot water tank (Y plan) heated by a conventional system Baxi Solo 2 60PF gas boiler (~20 years old) with a Grundfoss UPS2 pump and a combined 22mm feed/expansion pipe from a cold water tank in the roof. There are 11 radiators and 2 towel rails, I estmate about 160litre capacity plus a bit for pipes..

I have just replaced the radiators (removing existing sludge in the old radiators) and ran the system for about 3 days with 2 litres of Sentinel X400 to clean it. I then drained it and ran water until clean through several of the drain points but failed to run clean water throught the boiler, so some cleaner will be left in the boiler. I refilled adding 2 litres of X100 and ran it for a couple of weeks, but a lot of air seems to be generated. I noticed that the cold feed/expansion tank was occasionally becoming hand warm, presumably from hot air going up the expansion pipe (the tank is very well lagged). I checked the water and it is light brown/orange like marmalade in colour. There is no sign of water loss.

I am now cleaning it again and have added 1 litre of Fernox Heavy Duty Cleaner and am runnnig it for a week. There is still a fair amount of air being generated and a bit of scum is forming on the water of the header tank.

Any ideas please what is causing the excessive air and scum?
Is it normal for the header tank to become a bit warm with a combined feed/expansion pipe?
Is it OK if the water is is light brown?
Should I be emptying, refilling, bleeding and running it several times to flush it?
If I add more that the recommended 2 litres of X100 will this help to reduce the generation of air?
Could excess air be generated by the use of the rather more powerful UPS2 pump causing the water to release air that is trapped in the water?

Thanks for you advice?

 

[John.g]

I have 10 rads (oil fired boiler) with a combined cold feed/vent (attached) installed over 40 years ago and the system is spotless with some of the original rads, it would be very unusual to get any form of movement or any sludge etc in the header tank.
I have a isolation valve on mains feed to the header tank ballcock (which I normally keep closed) and on the very rare occasions that i have drained down the system I just crack open the isolation valve, my theory is that the air can pass up through the same pipe (and vent) that the cold feed make up is trickling down to fill the system, I don't have any particular problems with a lot of entrained air after a day or two.
I assume that when you say you have a combined feed/expansion pipe that you still have the vent carrying on up and over the F&E tank. I have seen systems without a vent and they are a pain to get rid of any air after drain down.

The UPS2 is a quite powerful pump, what setting is it presently on? and what model do you have?, does it have a display with LEDs?.

 

[Pirbrightgolfer]

Thanks. I was running the pump on the highest setting 3 but have just reduced it to 2.

this is a diagram of the piping around the tank and pump. Apart from the probem with the air the system works fine

I find that as air builds up in the radiators the water in the header tank rises, but this is to be expected. The vertical distance from the pump to the header tank is abut 1.5 mitres.

Grateful for any further thoughts, thanks
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PS - pump is UPS2 25-80 with green leds by the setting numbers I II III.

 

[John.g]

That's a massive pump, with enough power to supply around 3 normal houses, it just goes to show how a combined vent/cold feed can deal with, as speed iii is 8M, speed ii is 7m and speed i is 6M which is (way) more than adequate for your needs as it will maintain this head of 6M at a flow rate of 37 LPM ~ 2 times more than your requirements, so IMO speed i which still too high but should certainly help with your problem. I don't think your pump has any other modes of operation (like proportional pressure (PP) but have a look as one of these settings would be more appropriate for your needs.
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You may have that PP control on your pump, simply press the setting button for > 5 secs and the LEDs should start flashing then select speed i again, see how your rads etc heat up and if too slow go to (flashing) setting ii.

 

[Pirbrightgolfer]

That's a massive pump, with enough power to supply around 3 normal houses, it just goes to show how a combined vent/cold feed can deal with, as speed iii is 8M, speed ii is 7m and speed i is 6M which is (way) more than adequate for your needs as it will maintain this head of 6M at a flow rate of 37 LPM ~ 2 times more than your requirements, so IMO speed i which still too high but should certainly help with your problem. I don't think your pump has any other modes of operation (like proportional pressure (PP) but have a look as one of these settings would be more appropriate for your needs.
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You may have that PP control on your pump, simply press the setting button for > 5 secs and the LEDs should start flashing then select speed i again, see how your rads etc heat up and if too slow go to (flashing) setting ii.

Many thanks. I will turn it down to I now. I put in the larger pump a couple of years ago when we started building our extension. The reason was that we were adding 2 new radiators with long 15mm pipe runs. The old basic Grundfos pump already had difficulties in feeding all the radiators so something bigger seemed needed. The house and the central heating have been extended a bit several times and the initial design was for a smaller system.
I cannot see what else can cause the problem other than the pump or some remaining sludge in the boiler generating gas. Thinking about where the air comes from, A mountain bike mechanic showed me once how he coudl draw more and more air out of old brake fluid, so fluids can contain a lot or air and I guess the vigorous pump action tends to release it.
I iwll update you after a few more days. Thanks again.