D
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?
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?