Hi,
I know this has come up several times in the past, apologies for asking again.
Symptoms: DHW OK, CH demand causes boiler to light for about 30s, then it goes out. Top of CH flow pipe is hot, as are several pipes within the boiler casing, and the pump body. Return CH pipe does not heat up appreciably.
From what I've read, the likeliest causes are:
1) dripping hot tap syndrome; I've had this before, but now, when I cut off the house's main cold stopcock, it doesn't improve matters. This eliminates this as a possible cause; is that right?
2) faulty pump; this was swapped a couple of years ago for a CP61 (I'm not sure whether this is identical to the original fitting, or just equivalent). It has a black plastic octagonal nut in the centre, and when I loosen this, I hear a rapid clicking noise (at which point I tighten it up again!). This suggests to me that the pump impeller is spinning (and the clicking noise comes from the blades brushing against something I've moved). Does that seem right?
3) the favourite (I think); the wax divertor valve is not working correctly. I've removed the front part (the wax capsule head); there were black deposits (magnetite?) inside, and I cleaned all the parts by boiling in citric acid, and they're now pretty clean. I reassembled and refitted it (and eventually did it correctly, with the washers and O-rings in the correct positions so that the head wasn't leaking!), but disappointingly, it made no difference. I wasn't expecting it to cure it completely, but I'd hoped that getting rid of the deposits might have improved matters sufficiently to suggest I was on the right lines - at which point I'd have bought a brand-new divertor for about £100+.
It could of course still be the valve/wax capsule, and I wondered whether I could test it as follows: as I understand it, when the CH is working with no DHW demand, the wax in the capsule melts, expands and pushes the stainless steel pin out. This moves a two-part brass extension, and pushes a brass disk against the force of a coil spring, which allows the CH water into the CH flow pipe. So, if I add a few washers (perhaps 5mm?) on the stainless steel pin so that the brass extension is always further out, the valve to the CH flow pipe should be permanently open, and the CH should work normally (or better than it does at the moment). Would that be a reasonable method to diagnose the problem, or can you see any potential problems with this approach? (Especially safety problems, or risks of doing permanent damage to the boiler). Obviously it wouldn't be a fix, since it would disable the DHW from taking the full boiler capacity when required, but I would then be able to buy and fit the replacement valve with some confidence that I wasn't wasting £100!
Any advice would be welcome. And thanks to all those professionals who have answered similar questions in the past - your replies have been very informative as I've tried to work out what's going on with this *&@#% boiler!
Rob
I know this has come up several times in the past, apologies for asking again.
Symptoms: DHW OK, CH demand causes boiler to light for about 30s, then it goes out. Top of CH flow pipe is hot, as are several pipes within the boiler casing, and the pump body. Return CH pipe does not heat up appreciably.
From what I've read, the likeliest causes are:
1) dripping hot tap syndrome; I've had this before, but now, when I cut off the house's main cold stopcock, it doesn't improve matters. This eliminates this as a possible cause; is that right?
2) faulty pump; this was swapped a couple of years ago for a CP61 (I'm not sure whether this is identical to the original fitting, or just equivalent). It has a black plastic octagonal nut in the centre, and when I loosen this, I hear a rapid clicking noise (at which point I tighten it up again!). This suggests to me that the pump impeller is spinning (and the clicking noise comes from the blades brushing against something I've moved). Does that seem right?
3) the favourite (I think); the wax divertor valve is not working correctly. I've removed the front part (the wax capsule head); there were black deposits (magnetite?) inside, and I cleaned all the parts by boiling in citric acid, and they're now pretty clean. I reassembled and refitted it (and eventually did it correctly, with the washers and O-rings in the correct positions so that the head wasn't leaking!), but disappointingly, it made no difference. I wasn't expecting it to cure it completely, but I'd hoped that getting rid of the deposits might have improved matters sufficiently to suggest I was on the right lines - at which point I'd have bought a brand-new divertor for about £100+.
It could of course still be the valve/wax capsule, and I wondered whether I could test it as follows: as I understand it, when the CH is working with no DHW demand, the wax in the capsule melts, expands and pushes the stainless steel pin out. This moves a two-part brass extension, and pushes a brass disk against the force of a coil spring, which allows the CH water into the CH flow pipe. So, if I add a few washers (perhaps 5mm?) on the stainless steel pin so that the brass extension is always further out, the valve to the CH flow pipe should be permanently open, and the CH should work normally (or better than it does at the moment). Would that be a reasonable method to diagnose the problem, or can you see any potential problems with this approach? (Especially safety problems, or risks of doing permanent damage to the boiler). Obviously it wouldn't be a fix, since it would disable the DHW from taking the full boiler capacity when required, but I would then be able to buy and fit the replacement valve with some confidence that I wasn't wasting £100!
Any advice would be welcome. And thanks to all those professionals who have answered similar questions in the past - your replies have been very informative as I've tried to work out what's going on with this *&@#% boiler!
Rob
