Bubbling Central Heating System

Hi,

Next challenge with my new house (lucky I enjoy plumbing....)

Ever since wed moved in, there has been a lot of air in the central heating. So far, I have tried the following...

1=2E Bleeding all the rads many times. The only one with any air in is the one in the master bedroom and this needs bleeding every few days. 2=2E The automatic air vent on the feed to the hot tank coil was very corroded so I have replaced it. Curiously it has a little plastic cap on it which I have left open (closing it keeps the air there until you open it) - I assume this is correct? 3=2E I then though the boiler was over heating the water or the boiler stat had gone. When I turn the boiler heat controller (currently set at 2), the boiler seems to fire if I turn it up and go out if I turn it down.

Other information I have ascertained is a=2E when the boiler is on, you can hear the air bubbling through it and into the first rad on the run b=2E when I bleed the master bedroon rad, the water is very aerated to the extent that I can't get "normal" water through it c=2E when I removed some water from the system to change the auto air vent, the water was clear which I assumes means there is no inhibitor in it. d=2E we had our first gas bill the other day and it was huge (=A3260 for 7 weeks) this used to be our quarterly bill in the last house!!! We have a 5 bed house but the heating is off in 3 of the bedrooms and the main bathroom as we don't use them. e=2E the boiler was supposedly serviced by the previous owners in November. f=2E I can hear the air through certain rads and the supply to the hot water tank coil.

I thought that no inhibitor could be causing corrosion and hence the air but given I can hear it in the boiler and there is so much of it, I thought this was unlikely to be the root cause. Once I figure out the cause, I will need to put some in anyway but didn't think it worth while at this stage.

So in summary, I am now at a loss. Anyone got any cunning ideas as my wife is convinced the house is haunted?

thanks in advance....

Lee.

Reply to
leenowell
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wrote

Next challenge with my new house (lucky I enjoy plumbing....)

Ever since wed moved in, there has been a lot of air in the central heating. So far, I have tried the following...

snip............

Is it an open vented system - ie is there a small header tank in the loft for feed/expansion? If so check to see if water is pumping over from the boiler vent pipe. This is not uncommon and gives rise to lots of air and corrosion issues if left unresolved. Also look for any post by Ed Sirett and check out his heating links in his sig

Phil

Reply to
TheScullster

Next challenge with my new house (lucky I enjoy plumbing....)

Ever since wed moved in, there has been a lot of air in the central heating. So far, I have tried the following...

b. when I bleed the master bedroon rad, the water is very aerated to the extent that I can't get "normal" water through it

silly question but you are not doing it when the system is running are you?

Tony

Reply to
TMC

In answer to Phil's question, it is an open vented system - I will check the vent pipe.

As for Tony's question - to be honest I didn't think it made a difference so have been doing it when I had a chance so it could well have been running. What impact would this have? I guess I had assumed that once the air was in the top of the upstairs rad, it was there fore good until I bled it?

thanks both for your help

Lee.

Reply to
leenowell

wrote

You will have to check this in all modes of system operation. Pump over can occur for instance when there is hot water demand only. Make sure you give it a thorough test as this is the most likely point of air ingress. This all assumes that the ball valve hasn't stuck and allowed the header tank contents to evaporate of course.

With some piping arrangements, bleeding rads with the pump running can actually allow air to be drawn in. Best to bleed the system with everything off then run the pump a bit to push air round to rads. Then re-bleed and keep doing this until the moving air sound is no longer heard.

One other tip, manually open any zone valves after turning off an before bleeding - makes a big difference. Don't forget to switch them back to auto before powering up though

Phil

Reply to
TheScullster

thanks very much for your help so far....

An update on investigations which still has my central heating bubbling and gurbling away!!!

  1. I have checked the vent pipe anad so far despite willing water to come out of it, nothing yet. I have tried hot water only, heating only and both for a couple of minutes each. I have now wrapped some kitched role under the pipe to give it a more thorough test over a few hours.
  2. Thanks to Phil's bleeding technique, I removed a fair amount of air from the system but even with the pump off, the water out of the master bedroom rad is still aerated. Should I run this out until clear?
  3. The only diverter I can see is for the hot water. I switched this to manual when bleeding and have now restored it to automatic.

When running the vent tests after a good bleed of the rads, I noticed the following

  1. when I switched the heating off at the timer and left the water on, the boiler gave a large "burp" and I could hear big bubbles of air rising up.
  2. hot water only gives lots of squirting/ sloshing/ running water type sounds
  3. heating only (just after water only) gave a few bubbly sounds then pretty quiet.
  4. both together gave much like water only but I could hear a noise which I can only describe as when you have a full balloon and hold the neck such that a little bit of air can come out. It is that high pitched almost whistle
  5. It almost sounds like the boiler is "creating" the air on the hot water setting which may sound a bit daft?

Any help greatfully appreciated.

thanks again Lee.

Reply to
leenowell

This may seem stupid and I don't mean to imply stupidity but you *have* checked there's enough water in the header tank and that the exit from the header tank is not blocked, haven't you? I only ask because the symptoms are exactly what you get if the ball valve sticks and you run out of water in the header tank and I saw no mention of this in other posts.

Reply to
Bob Mannix

Bob,

No question is stupid as I am clearly missing something as I still can't get to the bottom of it.

The header tank is full and the supply pipe OK. In fact, I had to drain it when I changed the vent valve so know it is OK. Further investigations last night seemed to suggest that having heating and water on together seems to create the air.... The investigations were

  1. Run heating only for about 20 mins. Turn heating off and bleed the rads and run the water out of the master bedroom rad until the aerated water stopped. Turn heating only back on and all is quiet except for some slight banging/ bumping noises at the boiler. Run for another 20 mins and checked the rads - no air
  2. Same as above with the hot water only. No air when bleeding the rads and all quiet except for the same banging and bumping noise.
  3. Turn heating and hot water on. More noise at the boiler then went to bed.
  4. Woke up this morning with loads of air in the system again...

This is driving me mad.......

Thanks

Lee.

Reply to
leenowell

One more question....

If I am getting water being pumped back up the vent pipe, how would I know? Sounds a stupid question but would it be literally pumping in or a tiny dribble? The reason I ask is that I put some kitchen roll over the end of the vent pipe to see if *any* water was coming through and when I checked it, it was damp. Not enough for the water to be pumping through it and it could have been from some splashing from the ball valve when I was bleeding the rads. Thought I would check with the experts...

thanks

Lee.

Reply to
leenowell

...

If I recall correctly, you've inherited this system in the house you've just moved into. Did the previous owner mention anything (obviously not).

Probably a red herring, but: when we had our CH replaced some years ago, when we had an extension built, we had horrific bubbling problems. To cut a long story short: when I got a different CH engineer to look at the problem, he declared that the installer had coupled up the piping to the boiler wrongly (I seem to recall: put the feed into where the outlet should have been).

So my suggestion is to pay a CH engineer to look at it. You need a reputable one!

Repeat: could be a red herring. Good luck anyway.

John

Reply to
John

Hi Lee You kitched roll will get a bit damp because the water in the system expands as the system heats up and this pipe allows the expansion to take place, depositing some water in the Feed and Expansion tank. Without it you would end up pressurising the system unintentionally. Had you seen a raging torrent of water issuing from the vent pipe then this would have suggested the cause of your problems, as it is, I think the problem lies elsewhere. It is possible that the air is being sucked into the system via this pipe however, due to an incorrect siting of the vent pipe in relation to the pump. The vent pipe should be situated AFTER the pump which ensure that the vent pipe is not put under a negative pressure situation. However if the vent pipe is BEFORE the pump then the a suction force can be exerted on the vent pipe causing the phenomenon you describe. To test this try suspending a bowl of water directly under the vent pipe, switch the system on and see if the water level in the bowl reduces (you may have a better method for testing this e.g. hosepipe on the end of vent pipe into bucket etc). The only other cause I can think of is localised boiling in the heat exchanger but this would be the result of a immense build-up of scale, sludge etc and I can't see that this is the case given that the water you are bleeding from the radiators is crystal clear.

Hope this helps Luke

Reply to
Wingedcat

I will run the tests you suggest this evening and let you know the results.

The localised boiling may be any issue (given the funny noises the boiler makes) but it was supposedly serviced before we bought the property (in Dec) so would assume any limescale issues would have been sorted then. Is there a thermostat that could have gone? The dial on the boiler seems to work e.g. turning it down when the boiler is lit switched it off and turning it up when the boiler is not lit lights it.

thanks for your advice,

Lee.

Reply to
leenowell

I run Luke's test over night so the heating and hot water were on for about 5 hours last night and 3 hours this morning. The test I run was to bleed the rad then put 1 litre of water in a small paint kettle and suspend this over the header tank such that the end of the vent pipe was at the bottom so it was fully submerged in the water. Last night the heating was noisy but interestingly, this morning it was worse than ever. I bled the rad again - lots of aerated water then checked the paint kettle. Over the test period, it lost somewhere between 75 and 100ml (probably nearer 100ml). My initial thoughts were

  1. Is this loss significant enough or could it be due to evapouration? It was obviously cold over night so not sure about this one.
  2. If it was sucking in air from the vent pipe, wouldn't it now be sucking in water and therefore the extra noisiness this morning would rule this out? Having said that however, there would still be air in the vent pipe from before so I guess that is not conclusive?

I have also noticed that my pump has 3 settings and it looks like it is on full. The property is a 5 bed house so is this why it is on max?

Thanks in advance for any help in getting to the bottom of this one..

thanks

Lee.

Reply to
leenowell

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