Central heating problems - continued

[Charles Middleton]

Hi,

As requested by Andy Hall, ive put some pictures of my CH system on line on a friends web space...

pictures are reasonably large so apologies in advance for download times.

The original problem can be read on this thread ...

of orginal post below...

Hi,

My central heating system seems to be making a number of funny noises...

- The pump sometimes speeds up and slows down - this is accompanied with what I could call a vibration noise. Very low pitched and not very loud. More like its coming from the pipes rather than the pump.

- At irregular intervals a loud-ish gurgling sound comes from the radiator in the master bedroom. This is accompanied by a sound I would compare to water running into the radiator. Almost as if I had taken the (imaginary) cap of the top of it and poured water into it. A water on metal sound - like its filling up but its full of water which a quick unscrew of the bleed valve confirms.

- If you put your hand on the pipe work in the airing cupboard (when not) hot, around every second you can feel something almost like someone is tapping on the pipe - a slight movement. Perhaps "knocking" would be a good description.

... also ...

- The master bedroom radiator requires bleeding on around a two weekly interval.

The system is (I'll describe as not sure on the exact description), Gloworm Ultimate boiler, a [something] Gold pump, has hot water tank and a small header tank in the loft. Is this an "open vented" system? The hot water tank has a small tank on the top which I believe provides the head for the system.

Thinking about it, is it fare to say that the only mechanical part of the system is the pump so It might be worth replacing this? Thanks in advance,

CM.

[Andy Hall]

header tank is the 15mm one that comes down, bends near the floor and joins the 22mm below the pump. I would think that the flow from the boiler is the 22mm that comes up through the floor, branches forward and joins below the pump. THe 22mm going straight up (from which that pipe is teed) is probably the vent pipe. This is a reasonable way to connect these as they are close, both on the same side of the pump and no restrictions between boiler and vent.

Looking at CH2, the feed to the DHW cylinder coil is running horizontally and then to the top of the coil. However, there is a

15mm pipe going upwards from the bend on the right. Where does this go? Is it also up into the loft and making an additional vent over the header tank? I could see why this is done because of the arrangement of the motorised valve. Some means to let the air out is needed. It could also simply go up slightly and be capped with an air vent which is opened to let the air escape when filling. If it is going up and forming an additional open vent, then this could be an issue because it is on the other side of the pump. In that scenario, it is possible that there is pump over into the header tank. That would lead to more oxygen etc. being introduced into the system.

Could you go up into the loft and then get somebody else to put the system through its paces - i.e. change thermostats to make the boiler run etc? THis way you can check the behaviour of the vent(s).. There should be about 50-75mm of water in the tank above the feed connection point at the bottom when the system is cold - more when hot.

Try altering the pump speed and see if this makes a difference.

THe gurgles and swooshing noises are typical of air getting into the system and being pumped round.

I would investigate all of that thoroughly first.

Did you test the gas coming from the radiator vents?

[tarquinlinbin]

I would have some minor concerns about the relative positions of the cold feed and expansion pipes in that strictly speaking, I would not consider them "close coupled". Have you checked in case the cold feed is blocked?. To do this,drain some water off the system (see if there is a drain valve downstairs) and see if the ballvavle in the header tank operates to top up as it drains. If not,suspect a blocked cold feed in the area whre it connects to the system.

joe

[Charles Middleton]

Hi,

On CH2 the pipe going upwards from the bend on the right goes upwards and is then capped with an air vent as you say. I think its a good idea to go into the loft and see whats happening. Ive got a mate coming around on Saturday who knows a little and I'll put your comments into the mix and try and work it out. I'll also test the air coming out for hydrogen.

On CH2, the pipe from the left of the motorised pump must feed the radiators. However, where is the return to the boiler if this valve if only the hot water is switched on?

Also, why is the pipe from the left of the valve connected to the pipe going upwards from the pump?

I wonder why air gets trapped in this one radiator however? This is the last radiator on the circuit.

Also, consider this. If the air is moving around the system (you can hear it bubble through the boiler and a few seconds after that the pump starts cavitating - so it is moving around) then it must at some point go through the coil in the DHW tank. I appreciate this doesnt solve the cause of the problem but is it possible to fit some sort of bleed filter to the bleed valve at the 15mm pipe coming off the 22mm where it enters the cylinder?

In addition, if air is getting in then this must be pushing water out. I presume back into the expansion tank in the loft.

The only other thing I have noticed is that my towel radiator has a slight leek. A couple of little drips that does build up to around 2 table spoons fulls of sugar over the course of the weekend. Could this be the route of the problem?

One more question: which way would the water flow through the pump?

Unfortunately I work away all week so I am limited to looking at the thing in the limited time I get at home at weekends :(

CM.

[Andy Hall]

OK, makes sense.

The pipe coming across horizontally above the immersion is the return from the coil in the cylinder. I can't see completely but I guess it goes down through the floor behind the pump?

If so, then the return from the radiators will join it under the floor and then go to the boiler.

Oh yes, I can just about see it in CH3.

Hmm.. shouldn't be. Perhaps it's blocked off. If you have the system on DHW only, does the pipe to the left of the motorised valve get warm above this join? How about below the join between there and where it goes through the floor? Logically, this lower piece should only get hot with CH running. If there is a way across, bypassing the valve then the radiators would get hot whenever the ump runs.

It can happen anywhere- for example if the pipes slope under the floor.

You could fit an authomatic air vent in place of the bleed valve, but it's not really a good long term solution. It's best to find the problem and fix it.

With the pipe layout it shouldn't be. It could be that the roof tank is empty and letting air in.

It's possible that when the pump runs, air is sucked in here and when it stops, there is a small leak out.

Normally it's upwards in this configuration.

[Phil Addison]

Yes, that short cross pipe is odd, and I can't quite see for sure how it is connected. There is also a gate valve (1), visible in CH3, that appears to be in the CH flow from the left of the motorised valve. Is there any sort of valve in the short pipe? Another photo showing these points more clearly would be ideal, or at least a confirmatory description. Everything else appears to be as Andy describes it.

The hot water coil return also has a gate valve (2) which would be used to balance the coil, but is only appropriate if the motorised valve is a "3-way" type and the system controller allows for both CH and HW to be on together. My guess is that the short horizontal cross pipe is an incorrectly fitted attempt at a by-pass, and the gate valve (1) should be in it and not where it is (or seems to be - it's difficult to tell from the photos).

Regarding the gurgling noises, one cause could be a stuck ball valve in the header tank in the attic, causing the tank to gradually empty if there is a leak anywhere - and you say there is a small one. Andy has already suggested checking there is water in the header. Push the floating ball down and make sure this causes cold mains water to enter.

Phil The uk.d-i-y FAQ is at

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