Central Heating Concerns

[Charles Middleton]

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.

[Grunff]

Sounds very much like you have air in the system.

And that your are sucking in air somewhere at quite a high rate. This air then collects at the first convenient location - your radiator.

Ok.

Yes.

No, the pump is not the problem.

Air is being sucked in. There are many possible places where it could enter the system, but the most likely place is through the vent - the pipe which hangs over the edge of your smaller loft tank.

If this is the case, then you may be able to cure it by reducing the pump speed (there's a 3 way switch on the pump). But this will upset the balance of your system, and may lead to inadequate performance.

The best solution is to figure out where your vent pipe connects in the circuit, and relocate it to a better place. This is a design flaw in the system - the vent pipe is connected too near the pump inlet, so water gets sucked in though it.

[Andy Hall]

It could be the pump on its way out or perhaps air getting into the system.

There probably is *some* air, it's just that it takes two weeks to gather a noticable amount.

With the pump running? Otherwise pipes in another part of the system which are getting hot or cool and are expanding or contracting.

That's a fair bit and should be investigated.

Could you elucidate a bit more.

Do you mean that there is a small tank in the roof and then separately and somewhere else there is a HW cylinder with its own small tank separate to the first?

In any case it's an open vented system, but if you only had a single header tank on the HW cylinder doing everything then it probably means that you have a Primatic cylinder and the way to proceed is rather different.

It could be, but there may be other issues. Can you comment on the system first. Also important if you have a small separate tank in the roof is whether there is enough water in it. Also the relative positions of the vent pipe leading to and over this tank and the feed/expansion pipe going from the bottom. It's quite important to know where these join the main system, how far apart etc.

.andy

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[Charles Middleton]

Hi Andy, thanks for the reply. My comments are below ...

This is with the pump running.

That is what I meant. There is a small tank in the roof and the HW cylinder has a small tank on the top of it.

Hopefully comments above have clarified the type of system. I'll have to get into the loft and have a look at hte latter points. I'm away all this week so will need to have a look at teh weekend. To clarify ...

- The feed/expansion pipe: I presume this is what will "top up" the system and also keep it pressurised?

- The vent pipe - what is this used for?

CM.

[Andy Hall]

It could be that the pump bearing is knackered, but I wouldn't shell out for a new pump just yet.

That's good. In that case it's a conventional open vent system and you can do things to the primary (heating) water without impact on the domestic hot water.

Yes, but it's not a pressurised system in the sense that you might have read about pressurised systems. They are completely closed in. The only static pressure that you have is by virtue of the height of the small tank in the roof.

To let air out of the system and in the event of a boiler malfunction such that it boils, steam. Some people mistakenly call it the expansion pipe - it isn't.

The pipe near the bottom is called the feed/expansion pipe because it allows the system to be filled and as the water is heated, it can expand back up into the tank.

In a correctly designed system, these two pipes should join the main circuit within about 150mm of one another and definitely not on opposing sides of the pump. Sometimes they join at a little chamber called an air separator which is used to make convenient connections and get air out of the system.

If the connections are not to the right places, or are too far apart, then there is a pressure differential and either air is sucked down the vent pipe or water pumped over. You may have the first of these, but it's not so obvious to see as the pump over case. Often it happens when motorised valves are changing or when the the pump starts.

Another possibility is that there is too little water in the small tank and when cold some air enters the system down the feed pipe. Often this is because the ball valve is stuck and the cure is simple. When the water is cold you need say 50mm depth above the feed pipe at the bottom - no more because you need to allow for a rise in the water level with expansion.

It's possible that corrosion is happening in the system. That would be if there is no inhibitor and if the escaping "air" from when you vent is actually hydrogen and burns with a small blue flame.

The source of the gas/air in the system does need to be investigated and fixed. If you are into doing some plumbing, information on how to fix the vent arrangement if this is what it seems to be can be provided here - helpful if you can put some photos on a web site.

I wouldn't spend money on a new pump at this point, but it could be worth turning it down a notch as suggested and see if the venting and noise issues reduce. If they do, then you have your culprit.

.andy

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[Charles Middleton]

Didn't have time to take any pics over the weekend. Ill do it next weekend and create a suitably titled thread with a link to the pictures.

Thanks all for the help. Is it safe to test if the gas in the radiator is nitrogen by setting alight to it? What's the worst that can happen?

CM.

[Set Square]

If it's nitrogen, nothing!

In the more likely case that it's hydrogen, it will burn with a blue flame - but is unlikely to set fire to your house. Have a wet cloth ready in case you need to smother it.

[Andy Hall]

I guess you mean hydrogen. Charles.

You can test with a flame. Obviously move anything flammable likle curtains out of the way, and have a damp cloth handy. Then just open vent very slightly and apply small flame. If you get a blue flame it's hydrogen....