Yay - noisy central heating

[andruec]

For the past year or so I've been subjected to gurgling from my bedroom radiator and from the airing cupboard. The gurgling only occurs when the system first comes on and after fifteen minutes or so the only sound is the pump running. Usually it's just when the heating is on but this morning it also gurgled while it was just heating the water.

I recently changed the programming so that the hot water only heats in the morning so this all seems to have something to do with the system starting from cold.

Details of the system:
Open vented, over 20 years old. Boiler was replaced over ten years ago.

During the last 15 years it's had a new pump and three motorised valve replacements. The gurgle seemed to start after a BG engineer replaced the bleed valve in the airing cupboard. The old one had started to leak.

I've bled the radiators and got air out of my bedroom. Another radiator in a smaller bedroom seems to always need bleeding. Curiously the smaller radiator bleeds at pressure - the water squirts out nearly horizontal. All the other rads just dribble out. I've looked for leaks and couldn't find any. Or..well..I noticed the copper pipe where the bedroom lock shield is attached has some green staining. That was replaced when BG fitted a TRV to it (the only TRV in the house). I've tested it by wrapping tissue paper around it but not seen evidence of leaking on the paper.

Anyway I'm hoping for suggestions on the likely causes of this. Is it just air getting in through a leak? How come is only does it when starting from cold?

Thanks for your comments.

 

[45yearsagasman]

There are many causes for your symptoms.
Micro leaks
Air being drawn in down open vents
Gassing (Hydrogen) in system.
My first checks would be, is system pipework configured ok and is there air coming down open vent on start up. Gassing is easily tested for. Micro leaks are more troublesome to find. A pic of your airing cupboard pipework would help in pointing you in the right direction.

 

[andruec]

Airing cupboard:

Some good news - while moving towels out of the way I found a missing sock so that's good

Once or twice I've pushed open the loft hatch to see if the noise was coming from there but it never seems to be. I haven't yet actually gone up first thing in the morning though. The pipework is largely unaltered since construction and nothing other than replaced bleed valve (right of blue motorised valve) since before it started.

I assume therefore that it's 'damage' rather than a design/installation issue.

 

[45yearsagasman]

That is a poorly installed installation. Nevertheless, get a magnet and check the pipework all around the pump including that large copper vessel on the RHS. The cold feed connection pipe etc needs to be checked. If there is magnetic attraction to copper pipes then that indicates magnatite in the vicinity. If you have BG contract they will almost certainly rec a powerflush.
Another test is to hold a full jar of water over the open vent (in loft) and get someone to turn the system on and see if the water in the jar is sucked out and down the vent pipe. Do those tests and come back.

 

[andruec]

Okay: Nothing magnetic about any of the pipes. Water does not get sucked into vent pipe - air splutters out a bit. The vent pipe was quite close to the water in the tank though so I've propped it up on an old X100 container I found up there.

What makes you say it's a poor installation? I know the pipe layout is a bit convoluted but as far as I know it's the original system. Mind you I didn't notice until I saw the picture that the bleed valve is lower than the top of the cylinder which seems a bit odd, if not rather pointless.

 

[HERTS P&D]

How high is the vent pipe above the expansion tank?

Andy

 

[andruec]

How high is the vent pipe above the expansion tank?

Andy

When I climbed up there this afternoon the high point of the pipe was almost resting on the edge of the tank and the bottom of the pipe was about two centimetres above the water (the system was cold). It looked very odd. the pipe comes out of the top of the airing cupboard, turns horizontal then there's an unsupported one metre length taking it to the FE tank. At that point it turns back vertical to form the curve.

That horizontal run was actually sloping down. I've placed the plastic bottle of X100 underneath the far end of the run and that's raised the bottom of the vent pipe so that it's only just below the insulation of the FE tank.

If I had to guess I'd say that the top of the vent pipe loop is now nearly as high above the tank as the tank is tall.

 

[andruec]

Right, I have some figures for y'all

The top of the FE tank is 480mm above the top of the loft rafters. With the plastic bottle supporting it the high point of the vent pipe curve is 1m above the top of the rafters. In this position the end of the vent pipe is level with the bottom edge of the insulation over the tank. I don't think it can go any higher as it needs to poke through a hole in the insulation.

The plastic bottle is raising the pipe by about 150mm. If the vent pipe is allowed to flop freely (as it was before I went up yesterday) the end of the pipe sits about 20mm above the water when the system is cold.

This morning the system seemed a lot quieter. It's not conclusive though as it's a mild morning and the hot water hadn't been used very much so I doubt the system worked very hard. From looking around the web it does seem that the height of the vent pipe above the FE tank is important - could this have been the cause all along? Changes to the house structure could mean that the pipe is no longer self supporting so could explain why it only recently became a problem.

 

[andruec]

There was still noise there this morning - this time from the hot water cylinder more than the heating. There was the sound of gurgling/trickling from the pump and an occasional 'gloop' from the cylinder (not the loft).

I've just kicked the system into action (first time it's been on in four hours) and explored pipework and loft and it's all quiet. Even the pump is just quietly humming to itself.

So..what's so special about first thing in the morning that makes it gurgle? Does this tell us anything more?

 

[HERTS P&D]

Post some pictures.

Andy

 

[andruec]

Post some pictures.

Andy

Of anything in particular?



There's a picture of the plumbing in my airing cupboard earlier in the thread.

 

[gigz]

I can't see a vent for the coil, it should be where the pipe leaves the 3port and goes back down to the coil (might be there just cant see it) have you bled that ?

 

[andruec]

I can't see a vent for the coil, it should be where the pipe leaves the 3port and goes back down to the coil (might be there just cant see it) have you bled that ?

It's just to the right of the 3-port switch in the picture (it actually bends round and points into the cupboard rather than being vertical. I have bled it but only water comes out. I can't help noticing that it's actually below the level of the top of the cylinder which makes me wonder how much use it really is.

 

[D_Hailsham]

I can't help noticing that it's actually below the level of the top of the cylinder which makes me wonder how much use it really is.

I noticed that. There also seems to be an air separator to the right of the pump, but unfortunately it is obscured by the slatted shelving (hint ).

 

[gigz]

It does'nt need to be above the cylinder as long as its at the highest point of the pipework, the pipe that comes off the cylinder goes up to vent. At least it should