Massive airlock problem

[mintajalepi]

I hope someone can help. I'm desperate

I have a massive airlock in my heating/water system. I’ve had the pump changed (along with something else – a thermostat on the water tank I think) and had the boiler off the wall to ensure the heat exchanger is not clogged. All this was done 3 months ago and system was bled 3-4 times at the same time (all to get rid of an airlock). I also had the whole system power flushed at that time.

Since then, heating has got progressively worse - and the air lock is now back. I am now bleeding rads bottom-up every day. 99 times out of 100 there is no air in the rads. I regularly hear a crashing/banging in the system and can hear a gush of water from the overflow (?) into the header tank in the loft. Occasionally, say 20% of the time, the boiler goes to overheat. I then re-bleed the rads, shut the power to the boiler, wait 15/20 mins and restart. All then works but I will get the crash/bang.

Can anyone offer advice/help on what I should do next? The airlock resolution has cost me, so far in excess of £1300 and I can’t afford to blindly call people out anymore. I’d rather try to have lots of info/ideas so the engineer “thinks” I know a bit about this sort of thing and does not try to rip me off.

I have a 5 year old Baxi boiler (with, apparently, no drain off valve).

All help and comments appreciated.

Thanks.

 

[dextrous]

First thing I'd check is whether there is sufficient water in the FE tank and that the ball valve works properly.

 

[Burnerman]

Is the circulating pump actually running?
John

 

[mintajalepi]

Hi dextrous and Burnerman, thanks for the replies.

The FE tank in the loft is 3/4 full. Just went up to check it 2-3 mins ago (and as it happens, have just heard a whole load of water come out of the "overflow/vent" pipe into the tank). I'm expecting the overflow pipe to be used any day now to take care of the excess water in the FE tank...

I have checked the pump and seems to be running. Checked all the radiators a few mins ago and they are hot and I can hear the water "hiss" as it passes through the pipes. The engineer who visited on Thursday last week also confirmed the pump is ok (well, it should be - it was changed 3 months ago along with a thing under it that has some sort of "switch" to send/receive signals to the boiler).

Ah, and there goes another load of air/water into the FE tank. That's twice in 5 mins...

 

[Burnerman]

Can you - in the interim - turn the pump speed down, turn the boiler stat down, and check that the tank stat isn't higher than 60 deg?
Do you know if any motorised valves were locked open when the system was refilled?
John

 

[mintajalepi]

Hi Burnerman,

Tank stat is now set at 55. Boiler stat instead of being ~90% is now ~75%. Not sure how to reduce the pump speed. Listening to what the last engineer said is that I have a 3-speed pump and it was set at "2". The Pump is a "Wilo". It has a sort of big screw on the front. Next to that is a black unit with 3 settings and a "selector". The "selector" is pointing to "2".

I'm not a DIY person at all but can understand a lot of what gas/electric people tell me. By doing as you suggest what is the reason and what should I expect to see/happen?

Btw... the "switch" I refer to in a previous post has Honeywell written in it.

As always, thanks.

 

[Burnerman]

Hi I'm just trying to apply some logic from afar.....
If the hot water that your boiler is generating can be effectively dispersed, then there will be no need for water to be discharged from the expansion pipe - unless the pump speed is much too high.
I think that your boiler is generating too much hot water, maybe due to a faulty boiler thermostat (does the boiler shut down at regular intervals)
or the water is being prevented from circulating either to a pump fault or a motorised valve in the off position when it should be open.
Do you know if you have a manual bypass valve or an automatic one?
All the rads should be fully on, and when you turn the cylinder tank stat up or down you should feel a valve opening, allowing circulation through the cylinder coil.
I'd like to see the boiler turning itself down by its thermostat before the banging starts, obviously.
John

 

[mintajalepi]

(does the boiler shut down at regular intervals) or the water is being prevented from circulating either to a pump fault or a motorised valve in the off position when it should be open.

The boiler does, on occasion, go to overheat. Shutting the whoile thing down, bleeding the rads (downstairs first), waiting for ~15mins and then turning it all on seems to sort that bit out. The last time it went to overheat was Sunday. Between last Thurs and Sunday it went to overheat around 6/7 times. On that basis it appears as if it is getting better... I did notice it go to overheat after someone went for a bath but that does not appear to happen now - but I am watching it like a hawk...

The only time the boiler goes off (not overheat) is when the room stat tells it to go off as temperature has been reached. Note that I have TRV's on all rads except kitchen (where the drain off valve is) and the bathroom towel rail (which is off at the moment as one of the valves on that has a tiny leak)

Do you know if you have a manual bypass valve or an automatic one?

This is way above my head - but if you tell me where to look, and what to look for, I'll figure it out

All the rads should be fully on, and when you turn the cylinder tank stat up or down you should feel a valve opening, allowing circulation through the cylinder coil.

All my rads have a TRV on the right side. The left side valve I have turned to fully open on all rads (not great for balancing but I'm in a problem solving stage at the mo..). I will try the tank stat shortly to see if I can detect a valve opening

I'd like to see the boiler turning itself down by its thermostat before the banging starts, obviously.

(I frequntly see and hear the boiler coming on and going off but I have not detected whether this is preceded by the banging.) By this, do you mean the boiler shutting down before banging starts (i.e. a signal controlled shutdown) or boiler going to overheat before banging starts. Could be difficult to get a grip/pattern on this one - but if it means all night in front of the boiler with the heating on to listen for banging and boiler going off etc then I'll do it...

Again, thanks.

 

[Burnerman]

The bypass is a pipe loop that connects the flow and return pipes from the boiler together (before the rads)...so that if all rads are off for some reason, the hot water can circulate back to the boiler. Often, the bypass incorporates a radiator that is left on all of the time, to disperse excess heat. This rad is often in the form of a towel rail or similar....we need warm towels all year round! Do you think you could have turned the bypass loop off....? I'd turn that towel rail back on.
I'd hope that the boiler would shut itself down before the banging starts - but if your system could disperse all of that excess heat then you'd be getting somewhere!
John

 

[mintajalepi]

Could the bypass not be the kitchen radiator with the drain off valve? This one does not have a TRV so would always be permanently on. It also happens (from what I have noticed) to be the first radiator to warm up.

May just have to get an engineer round to tell me what kind of bypass I have. I have no way of telling. In any case, I would have to assume it is manual on the basis that a) an automatic one would cost more money and b) I know I would not have spent that money when I had a new boiler and radiators (and ~20% of the piping) installed about 5 years ago.

I might have to call a very competent mate on the weekend to drain off the system and refill it (adding some inhibitor) so that I can replace the leaking valve on the bathroom radiator and then leave it on. Only issue is that it gets b****y hot and will burn my 2 year old if he touches it...!

What I just noticed is that the boiler has 4 lights: Overheat, Boiler On, Fan On, Pilot On and Burner On.

When the boiler overheats only the Overheat lights up.

When the boiler fires up for water or for heating, all lights except Overheat light up. This makes sense to me.

What I have just seen is that the Boiler On light is lit - but none of the others are. I previously have seen none of the lights on. So, I'm not sure of the significance of the situation of all lights off versus just the Boiler On light being lit.

I also turned up the tank stat from 55deg to 70deg. There was a noise generated as it went past 60deg but I didn't hear it again when I went back down to 55deg.

I also noticed that a lot of the pipes in the cupboard where the tank, pump and Honeywell-thing are very very hot. You can't hold them for more than a fraction of a second...


Thanks

 

[mintajalepi]

Since yesterday I have noticed that the boiler goes off and then I hear the banging followed by a load of steaming water gushing into the tank.

When I say the boiler goes off I mean all the lights go out.

 

[Goldspoon]

If you follow the pipe that comes from the top of your coil (from your cylinder) does it go to the vent pipe?

I ask because usually the top of the coil is the high point where air collects and it should all escape via the vent (preventing air locks).

Also does this happen when you are on hot water only or central heating?

 

[mintajalepi]

Sorry for not replying to posts earlier. Have been away.

Goldspoon - I cant trace the pipe from the cylinder so can't tell where it goes. The banging happens 99% of the time with just heating on. I can't tell whether having the hot water on at the same time affects it.

Since my last post I have:

1) Filled the FE tank manually to 3/4 full.
2) Run the heating for 30/40 mins and turned it off
3) Bled the rads bottom up. I have not been able to bleed the pump as I don't know how to
4) Whenever I hear any banging I turn the system off and bleed the rads

Over the last couple of days I have noticed that:

1) Each day, the banging has got progressively worse. Yesterday evening the boiler went to overheat for the 1st time in a couple of weeks
2) I shut the whole thing down and checked the FE tank. It was 1/3 full (meaning water had been fed into the system) so I manually topped it up to just over 3/4. (The overflow on this is tank is about 2 inches above 3/4
3) I bled the rads
4) Turned the heating on

It has been working and the boiler has not gone to overheat - but the crashing remains.

This morning (while putting the rubbish out) I though I heard water coming out of the overflow pipe. When I was in the shower I actually saw water coming out of the overflow pipe. I guesstimate this to be around 1/2 pint. This tells me that

1) When the banging starts and the boiler returns the hot water to the FE tank it overflows
2) The return of water to the FE tank **must** mean that the water expelled by the boiler into the FE tank needs to be replaced
3) If the FE tank is overflowing then it **must** mean that the cold water feed to the boiler is not working...? But... it was before as it went down from 3/4 full to 1/4 full...

I am now thinking of having the whole system drained and powerflushed. God alone knows what that will cost. Any ideas as to reasonable cost?

I am also now thinking of having a "pressurised" heating system installed in the loft and doing away with the FE tank. I have read that you need to have a "spot-on" basic system (right pipes, no sludge etc) as a pre-requisite. Any ideas what this means and what a likely cost could be?

As always, I appreciate the help you all offer to this desperate novice.

Thanks.