Radiator needs daily bleeding

[Deleted member 77550]

Hi,

I have a CH problem which I've done a bit of diagnosis on, but am stuck with what to do next. I'm a DIY-er, not a professional - I have no problem calling a heating engineer in, but want to see firstly if it is something I can fix myself, and secondly have enough info to give the engineer to make his/her fix a bit quicker!

Sorry for the long post, but I thought I'd try to answer any questions before they are asked!

I have an open vent system, potterton netaheat boiler (old, but no problems with it for the last 10 years other than a replacement fan), feed & expansion tank in loft, hot water cylinder in airing cupboard, with 3-way diverter valve (honeywell) and pump (grundfos) next to it. I have a towel rail radiator that comes on whenever hot water or CH is on, other rads only on when CH requested. Last work on the system was summer last year when a replacement rad was added. System was then flushed, inhibitor added and has been working ok all winter so far.

Cutting a long, boring diagnosis story short - starting a couple of days ago the towel rail radiator now needs to be bleed daily and seems to empty of water - it takes about 15 minutes to bleed, as it seems completely empty (cold right from the bottom, heats up slowly to the top as being bled). Boiler is cutting out completely (without any rads getting hot) as I'm guessing it has just air in the system and shuts down due to it's protection circuits. When I start to bleed the rad and water starts to circulate, the boiler kicks in again and works ok. The pump seems to get very hot, but I don't know if this is unusual or not.

The expansion tank in the loft has water in it, and the ball cock works ok - i.e. it tops up automatically if needed. The water in it is a little red-sludgy though.

I've match-tested the air coming out of the rad - it seems to be air rather than hydrogen.

If the heating is on, some air seems to be getting in, but not too much - i.e. if I bleed the rad fully, have the heating on for a few hours, and re-bleed, there's only a few seconds of air in the system. However, if the heating is off, by the time it is next scheduled to come on again (maybe 8 hours later), the rad is empty again (and the boiler therefore doesn't work, and all rads are cold, though I do get a bit of hot water, so I guess it heats for a short while).

None of the other rads need bleeding, just the towel rail, which is at the highest point in the system.

I can't see any leaks of water anywhere around the home. It could be under the floorboards somewhere, but with that amount of water being lost, I'd have thought I'd spot that! No water or drips anywhere in the airing cupboard, including around the pump.

I try to bleed the rad with the heating off, but after a few seconds of air, nothing seems to happen (it may be bleeding very slowly I guess). With the heating on, it seems to bleed quicker (pump increasing pressure in the system?), plus you can tell it's bleeding as the hot water moves around the rad!

The pump works (I can hear it), I assume the diverter valve works (as if I select HW only, only the towel rail heats up, if I select CH then all rads heat up - both times after having to bleed the rad of course), the boiler seems to be working ok (once the rad is bled, it kicks in and shuts off as usual - i.e. with the timer or thermostat as needed).

Any suggestions as to what it may be, or what I can try next to diagnose the problem?

 

[gassafe]

System could be pumping over & bringing in air... Could be a leak in the system if th rad is draining as you say... Maybe the cold feed is blocked too... Needs checking out by a heating chap!

 

[stevetheplumber]

check for a blocked cold feed does the tank empty if you drain a bit from the system

 

[bright spark]

Don't think ye'd b able to vent the rad if cold feed blocked. System is either pitching or leak. Could b under the floor or could be slight leak on boiler when running from heat exchanger. If your venting that rad regularly, I think you might need to get a guy in

 

[joni os]

Isolate towel rail, valves both sides and see what happens.

 

[Deleted member 77550]

Thanks very much for the quick replies. Water feed into the expansion tank is fine - pushing the ball cock down a bit and water comes in no problem. I haven't checked if the water is actually being topped up (will try stopping the water feed in, and seeing if the water level goes down) - I didn't know what that would tell me either way, but it's all info to pass on to the engineer that it's looking like I'll have to call out!

I'll isolate the towel rail, thanks for the suggestion, though not sure how I can tell if there's air in the system after that - but if the rest of the system doesn't heat up and the boiler cuts out, then I guess that would imply the problem is still there. Presume that if the problem goes away with the towel rail isolated, there must be a leak in that somewhere (though I can see all the pipes into and out of that, and no dripping).

 

[macackau]

Unless you are going to watch the f & e when you isolate its water supply don't do it. You could do more harm than good. If there is a leak the system could run dry and then you'll be in a world of hurt. Best bet would be to drain the system a little via a hose pipe attached to a drain off valve and see if the f&e tank starts topping up the system.

 

[gassafe]

Isolate towel rail, valves both sides and see what happens.[/QUOTE

I'm not sure what that will prove...

If the system dosent fill without the pump running then it could be a blocked cold feed or partial blockage... Although it would eventually fail to fill completely... Must be pretty bad for it to stop the boiler operating... Could be a leak under your floor

 

[joni os]

As the towel rail is only rad that needs bleeding, isolation would confirm problem is elsewhere.

 

[harrygashull]

Likely to be a poorly designed fill and expansion in conjunction with sludge, caused by a poorly designed fill and expansion...

 

[Swizz]

Sounds like your pump is pulling air from the expansion pipe that goes to the F&E tank.
Maybe this is why the pump is getting so hot.. could be burning the pump out while sucking in air.

Also turn the pump speed down, sometimes a high speed setting can cause air bubbles.

Potentially the system is over pressuring causing the expansion pipe to kick out excess water volume.. Keep an eye on your F&E tank over flow pipe.

 

[Deleted member 77550]

Well, I thought it may be useful to provide an update to the problem, as it has been a couple of months now....

Following advice received on this forum, and thinking that the last thing I could try before getting a heating engineer in, would be to drain the system completely and refill it with cleaner, run for a week, then refill with inhibitor and see what happens - worst case it doesn't fix the problem and the whole thing would need to be done again by a heating engineer and I'd be £20 out of pocket, but at least it would be more info to pass on to the engineer.

System was fairly slow to empty, but not excessively so (in my limited experience!) - with all bleed valves open took about 20 minutes (7 rads in the system). Water came out a little murky, but not too bad, and no lumps of anything. It did drain the F&E tank, so there was obviously no complete blockage in the cold feed. However, filling the system took AGES - took about an hour to fill the downstairs 3 rads, another hour to fill the upstairs 3 rads and another 40 minutes to fill the towel rail (higher up). So I'm thinking maybe a partial blockage somewhere? Added cleaner and ran for a week, hoping that would clear it. I also turned the pump speed down from its middle setting (of three) to its lower setting. The problem didn't appear that week, and the rads still warmed up nicely, so the lower speed setting on the pump didn't introduce any more problems. I did notice that the pump on the higher setting did seem to overflow a fair bit (the F&E tank got cloudy after a couple of days, implying it was overflowing into there) - when I turned it down, this was lessened (it still got cloudy, just a lot slower). After draining and refilling again (it still took ages to refill), it has now been working (at the lower pump speed) without the need for excessive bleeding for the last few months.

So the advice was probably right - I expect a slight blockage on the cold intake from the F&E tank, and the pump was pumping over and air was being sucked in. Still not sure where the air was getting in. I don't think I've fixed the problem - probably just worked around it for a bit. I guess the system would need a complete power flush to fix? Can't afford that right now. Will just have to keep an eye on it. At least it looks like there wasn't a leak

Thanks all for your helpful advice.

 

[Howsie]

Thanks for coming back with an update. So many people just take the free advice and run.

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