I have an intermittent boiler venting problem which has proved difficult to diagnose.
Background: I have lived in the same house for some thirty years, and the core pipes (I believe they are cast iron, and quite thick) for the heating system must be at least 10 years older than that. Various radiators have been replaced over the years. Anti corrosion liquid has been added whenever the system had to be drained. The oil fired system serves 17 radiators in four bedrooms and three reception rooms (though never are they all heated at once).
A conventional boiler was replaced by a condensing boiler (with a magnetic filter) with a rating of 90-120 (the same as the previous boiler) in November 2018. I believe that prior to that replacement the hot water system was gravity fed. Now there are motorized valves (but no thermostatic room controls). The hot water tank was replaced about four years ago following a leak. The pump was replaced earlier this year, and the system has been much more silent since the new pump was fitted.
For just over a year the new boiler functioned just as well as the old one. It was fitted by someone who had done work for me before and whom I regarded as trustworthy; but on this occasion I found his general performance less satisfactory – delays, postponements, undue haste etc. He has been difficult to contact since then, and I have lost confidence in him.
The day after it received its first annual service the pump sprang a leak, and the joints had to be re-fitted. The following day the boiler vented hot water into the header tank. I presumed that this was a coincidence (my wife was less confident!). I was advised to keep the pump running slow, and to ensure that not too many radiators were turned off. I did this, with no further problem. Except that on the only two occasions when I ran the system on hot water only (by accident: - this is not something I normally need to do) the system vented into the header tank, which overflowed.
Yesterday the heating was off for a few hours while we were out. We switched the heating on again, and about 20 minutes afterwards with much gurgling and banging the system vented again. The boiler was obviously very hot. When it cooled we put the heating on again – nervously! – and it has functioned normally since then (I took the precaution of turning on some extra radiators, though when the venting happened there were no fewer radiators on than had been the case earlier, when all functioned normally).
I am at a loss to understand why it should have vented after functioning normally for some time, with no difference in settings or circumstances. But I am left feeling nervous!
I have sought advice from two local plumbers, but they cannot offer an explanation.
Could it be that the boiler is too powerful? I was told that a lower output would be adequate, but the new boiler is the same rating as the old one.
Another thought: there was a gateway valve fitted to the hot water tank when the new boiler was put in. Is it possible that this is set too low, and not enough flow is getting through to the hot water tank? Might this account for the problem? (I could always open the valve a little, but I am reluctant to adjust setting which I do not properly understand; and anyway, why should this be a problem so intermittently?
For completeness: there is one radiator (upstairs) which I find I have to vent very frequently – which may indicate a leak somewhere?
It has been suggested to me that a full power flush of the system might help. Is this worth trying? Any downsides to doing that?
Background: I have lived in the same house for some thirty years, and the core pipes (I believe they are cast iron, and quite thick) for the heating system must be at least 10 years older than that. Various radiators have been replaced over the years. Anti corrosion liquid has been added whenever the system had to be drained. The oil fired system serves 17 radiators in four bedrooms and three reception rooms (though never are they all heated at once).
A conventional boiler was replaced by a condensing boiler (with a magnetic filter) with a rating of 90-120 (the same as the previous boiler) in November 2018. I believe that prior to that replacement the hot water system was gravity fed. Now there are motorized valves (but no thermostatic room controls). The hot water tank was replaced about four years ago following a leak. The pump was replaced earlier this year, and the system has been much more silent since the new pump was fitted.
For just over a year the new boiler functioned just as well as the old one. It was fitted by someone who had done work for me before and whom I regarded as trustworthy; but on this occasion I found his general performance less satisfactory – delays, postponements, undue haste etc. He has been difficult to contact since then, and I have lost confidence in him.
The day after it received its first annual service the pump sprang a leak, and the joints had to be re-fitted. The following day the boiler vented hot water into the header tank. I presumed that this was a coincidence (my wife was less confident!). I was advised to keep the pump running slow, and to ensure that not too many radiators were turned off. I did this, with no further problem. Except that on the only two occasions when I ran the system on hot water only (by accident: - this is not something I normally need to do) the system vented into the header tank, which overflowed.
Yesterday the heating was off for a few hours while we were out. We switched the heating on again, and about 20 minutes afterwards with much gurgling and banging the system vented again. The boiler was obviously very hot. When it cooled we put the heating on again – nervously! – and it has functioned normally since then (I took the precaution of turning on some extra radiators, though when the venting happened there were no fewer radiators on than had been the case earlier, when all functioned normally).
I am at a loss to understand why it should have vented after functioning normally for some time, with no difference in settings or circumstances. But I am left feeling nervous!
I have sought advice from two local plumbers, but they cannot offer an explanation.
Could it be that the boiler is too powerful? I was told that a lower output would be adequate, but the new boiler is the same rating as the old one.
Another thought: there was a gateway valve fitted to the hot water tank when the new boiler was put in. Is it possible that this is set too low, and not enough flow is getting through to the hot water tank? Might this account for the problem? (I could always open the valve a little, but I am reluctant to adjust setting which I do not properly understand; and anyway, why should this be a problem so intermittently?
For completeness: there is one radiator (upstairs) which I find I have to vent very frequently – which may indicate a leak somewhere?
It has been suggested to me that a full power flush of the system might help. Is this worth trying? Any downsides to doing that?