I have a problem with my central heating system, which I hope someone could advise me on. I'm not very good with plumbing, so if I am lacking info, please forgive me and ask for more details.
Anyway, My central heating pipes/rads make quite a lot of noise of running water, particular upstairs and in the pipes going to upstairs. The radiators upstairs are a nightmare. One of them is relatively ok, heat-wise, but it needs bleeding every 2 or 3 days. The other radiators are cold and appear to be empty. If I open the bleed valves on these with the thermostat set so the pump and heating is running, then water drains from the radiator (I can feel suction on the bleed valve.) If I turn the thermostat so the heating is off, the radiators fill up, but when they are full, they are still cold (getting full with cold water??) Sometimes, through bleeding all rads at the same time and then switcing the bleed valves off, I hear running water, then the header tank overflow pipe starts spilling water. And that's about it, I'm not sure where to begin to look.
Does anyone have any ideas or suggestions. I'm quite prepared to call a plumber out if that's what's necessary, but I'd prefer to know what the problem is before I did that so he can't try pulling the wool.
Has it ever worked? Has this problem arisen since someone did some alterations or repairs to the system?
My first thoughts are that the pump is pumping in the wrong direction - and needs turning round. But we really need more details of the system type.
Are both heating and hot water pumped, or is HW primary circulation by gravity (convection)? Are there any motorised valves? If so how many, and does each one have two or three water connections? [Photos of the pipework in the airing cupboard - if that's where the valves/pump are - would be useful].
Which header tank is overflowing - the large cold tank which feeds the domestic hot water system, or the small tank for the heating system? If it's the small one, is the ball valve working ok? What is the water level when the system is cold? [There should be only 2 or 3 inches of water in the tank - with the level a *long* way below the overflow to allow for expansion].
It has worked much better in the past than it does now, although problems seem to come and go. The upstairs rads have always needed frequent bleeding, and the system has always been noisy, in terms of running water. There hasn't been any work done, other than a boiler service a year or so ago.
My system consists of a Baxi Bermuda located behind my gas fire downstairs. The pump is under the downstairs floorboards. I think (but I'm not sure, sorry) that the HW is circulated by gravity. I really couldn't answer about the motorised valve. I haven't noticed any around the pump or in the airing cupboard, but this doesn't mean there aren't any (it's generally inconvenient getting to the pump)
It's the small one that is slightly warm that sometimes overflows (but hasn't done for some time.) The ball valve is fine, and the water level is normally well below the outlet.)
I used to be able to bleed the radiators with the pump running in the past, but like I said, if I do that at the moment, the rads appear to drain. Where could the water be going? I haven't spotted a leak anywhere (and I did look under the floorboards too :)
I appreciate the help, if there's any more info I can give, I'll gladly do so. Many Thanks, Bob.
OK, it's almost certainly gravity HW circulation (two 1" or 28mm pipes connected to one side of the boiler and going to the indirect coil in the hot water cylinder in the airing cupboard) and pumped CH (two 3/4" or 22mm pipes connected to the other side of the boiler). Presumably there's no cylinder stat, and the DHW gets hot whenever either HW or CH are switched on, and sometimes gets *too* hot?
I would guess from your further information that you have no corrosion inhibitor in your system - with the result that a lot of sludge has built up, partially (or even completely!) blocking some of the radiators. I would also guess that what you are bleeding out is hydrogen caused by the corrosion rather than air. [You can test for this by holding a lighted taper in the stream of gas coming out of the bleed valve. If it burns, it's hydrogen!]
Sludged-up radiators would probably explain what happens when you try to bleed with the pump running. The pump is probably installed in the boiler return - so that it's in effect sucking the water through the radiators. If the inlet of a radiator is blocked, and you suck on the outlet with the bleed valve open, you're going to suck the water out. This will end up in the header tank, with a resulting rise in level.
It seems to me that your system needs a really good flush out, and then needs to have inhibitor added. By far the best way to flush it out - particularly with summer coming on - is to remove the rads and take them outside and give then a good flush out with a hosepipe. While they're off, flush the flow and return pipes by keeping the header tank full and opening each radiator valve in turn (with a bowl under it to catch the water!). Incidentally, take great care not to spill any black sludge from the radiators on your carpets - it makes a pretty indellible dye!
If you get a plumber in, he'll probably want to charge you an arm and a leg for doing a power flush. However, the method I have described is far cheaper - and probably more effective.
That's fantastic information, many thanks Set Square, I'll give that a go. Incidentally, with me being a complete newbie, where does one put the corrosion inhibitor? Does it simply pour into the header tank?
Yes. After flushing it out, drain and re-fill the system. Part-way through the fill process, pour in the inhibitor. It will then get thoroughly mixed in.
Right, finally had a go at the first radiator....unfortunately the results weren't as I was expecting from your description.
I took a rad off and flushed it out, and as expected was a bit mucky, although not really sludgy. I then opened a valve on the pipes (not sure which is flow and return, so did each separately.) Anyway, when the pump was off, I got water flowing, which I let run until it ran clear. However, when I switched the pump back on (by turning up thermostat) the water stopped flowing and I could feel the suction at the valve again. The same symptoms occurred at both valves. By the way, I closed the valves on all other upstairs rads.
Is this what you would expect or is something else wrong. Additionally, is there anything else I can try?
Remind me of the original problem - it seems a long time since I wrote the above!
A description of the system - including the relative position of boiler, pump, zone valves, etc. would help. Even better if you can take some photos and upload them to a website and post a reference to them.
Here's the description I posted first time, aswell some other bits I posted:
My system consists of a Baxi Bermuda located behind my gas fire downstairs. The pump is under the downstairs floorboards. I think (but I'm not sure, sorry) that the HW is circulated by gravity. I really couldn't answer about the motorised valve. I haven't noticed any around the pump or in the airing cupboard, but this doesn't mean there aren't any (it's generally inconvenient getting to the pump)
Anyway, My central heating pipes/rads make quite a lot of noise of running water, particular upstairs and in the pipes going to upstairs. The radiators upstairs are a nightmare. One of them is relatively ok, heat-wise, but it needs bleeding every 2 or 3 days. The other radiators are cold and appear to be empty. If I open the bleed valves on these with the thermostat set so the pump and heating is running, then water drains from the radiator (I can feel suction on the bleed valve.) If I turn the thermostat so the heating is off, the radiators fill up, but when they are full, they are still cold (getting full with cold water??) Sometimes, through bleeding all rads at the same time and then switcing the bleed valves off, I hear running water, then the header tank overflow pipe starts spilling water. And that's about it, I'm not sure where to begin to look.
Your original reply read:
I would guess from your further information that you have no corrosion inhibitor in your system - with the result that a lot of sludge has built up, partially (or even completely!) blocking some of the radiators. I would also guess that what you are bleeding out is hydrogen caused by the corrosion rather than air. [You can test for this by holding a lighted taper in the stream of gas coming out of the bleed valve. If it burns, it's hydrogen!]
Sludged-up radiators would probably explain what happens when you try to bleed with the pump running. The pump is probably installed in the boiler return - so that it's in effect sucking the water through the radiators. If the inlet of a radiator is blocked, and you suck on the outlet with the bleed valve open, you're going to suck the water out. This will end up in the header tank, with a resulting rise in level.
It seems to me that your system needs a really good flush out, and then needs to have inhibitor added. By far the best way to flush it out - particularly with summer coming on - is to remove the rads and take them outside and give then a good flush out with a hosepipe. While they're off, flush the flow and return pipes by keeping the header tank full and opening each radiator valve in turn (with a bowl under it to catch the water!). Incidentally, take great care not to spill any black sludge from the radiators on your carpets - it makes a pretty indellible dye!
Sorry to make the post so long, I just thought as most of the info was there, I'd just cut and paste.
I'm not sure what to take pictures of to be honest, as I said, the boiler is behind the fire, and the pump is under the floor. That only leaves the airing cupboard & header tank...
Ah, I remember the one. With a Bermuda and gravity hot water there won't be any motorised valves - so don't waste time looking for them.
It still sounds as if there is a blockage on the flow side of the CH circuit. Are the downstairs rads ok? When you flush the pipes out with an upstairs rad removed by opening each valve in turn (with the pump off, of course) do you get a good flow from *both* valves?
Are the HW and CH circuits separate, or do they share any pipework? If it's like the Bermudas which I used to own, the boiler casting will have 4 connection points - 2 on each side. It works best if the HW circuit is connected to one side and the CH circuit to the other - but you sometimes find them both connected to the same side, and then splitting into 2 circuits.
Is this a recent problem, or has it *never* worked properly?
From the "suction" with the pump running I'd be immediately suspicious of a pump installed in the return from the radiators. The suction will lead to air being drawn into any weakness point (valve glands, pipe joints etc). To the OP can you see an arrow on the body of the pump or identify which way the water flows through it and see if it is pulling water away from the boiler or pushing it back towards it? A continuous slow ingress of air (oxygen) will lead to corrosion and the production of sludge which will settle out at points of low velocity and eventually cause circulation difficulties.
Flushing out everything and then a dose with Sentinel Ferroquest and a hot circulating flush will help no end
Dont spill anything on soft furnishing or Set Squares prophesy will come true
Downstairs rads are fine, never need bleeding, and kicking out plenty of heat. I'll have to get back to you on the flow from both valves question....all rads are back in place for the moment.
As far as I can tell, they are separate. There are four pipes coming out of the side of the chimney breast running to upstairs (HW F/R & CH F/R???). I only know that all pipes come out of one side of the chimney breast, not sure how they are configured at the boiler itself.
The upstairs rads have always needed bleeding very regularly, and have always been quite noisy. It's only recently (12-18mnths) that they appear to empty with the pump running.
Again, thanks for the assistance. It's much appreciated. Bob
As long as we've lived in the house, the pump has never been removed or replaced. I will do what John suggested and get under the floor to check the flow direction and report back. I'll also flush all the upstairs rads, and let you know about the flow rate from each valve.
Thanks for the reply John, I'll flush the other rads, and check for the arrow on the pump....it's pretty inaccessible, under the floor, unfortunately.
Incidentally, you mention air being drawn into weak spots in the pipework if the pump is pulling rather than pushing. If it were pushing, would I notice water coming *out* of these weak spots?
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