combi boiler leaking through condensate pipe

[merluzzo]

A while ago I posted about my boiler (Worcester/British Gas RD 542i) losing water pressure

After several experiments, I eventually realised that the missing water goes away through the condensate waste pipe. This PVC pipe is connected to a hidden waste pipe behind the shower, which is why it took me so long to identify.

Reading around, I understand that this may indicate that there is a leak in the heat exchanger.

Some people also say that if this is the case it is probably not worth repairing the boiler and installing a new one could be the best option.

I would be most grateful if somebody could advice on how accurate the diagnosis is (that the heat exchanger must be responsible) and, if this is the case, if it makes sense to have it repaired by a gas engineer or not.

[kempiejon]

I found a dripping drain off valve in the cupboard under the stairs, it had flooded and soaked into the carpet and some mould had grown on the walls so it must have been dripping for weeks. Having repaired that by tightening the screw a half turn I topped up the system and kept and eye on the pressure. Even with the drip repaired the pressure would decline over time. Although the system was losing pressure it was still working OK as far as I could tell - hot water and rads. But the little gauge was often in the red, so I'd refill and bring the needle back into range. I checked and found the water loss was now coming through the condensate waste pipe - slow rate couple of drips a minute and not all the time. I solved the problem with occasional filling. When I got the fella round for the annual service (the second in 4 years) I commented on the drip and he said it could be loads of things but proceeded to check the system while servicing and he found it* needed pumping up with his bicycle pump. The service fella said that'd probably be it but there might be another problem hiding behind the low air pressure so I should call him back if the problem re-occurred. Since then, over a year ago I've re-filled a couple of times and this post has reminded me not to forget to have it serviced again.

*Expansion vessel that's what I think it was called.

IANAP/HE

[merluzzo]

Thanks Kemplejon,

I know faulty or flat expansion vessels can cause loss of pressure, but I excluded that as I replaced it a week ago (as suggested by a plumber as first thing to try) and it has not solved the problem.

I also checked the copper pipe that goes outside (and that I believe is connected to the pressure relieve valve) and is not leaking significantly.

Finally, I tried the waste condensation pipe (had to cut it to check) with the boiler off and the pressure at 2.5 bar.

It leaked around a pint of water in three hours.

[kempiejon]

Thanks Kemplejon,

I know faulty or flat expansion vessels can cause loss of pressure, but I excluded that as I replaced it a week ago (as suggested by a plumber as first thing to try) and it has not solved the problem.

I also checked the copper pipe that goes outside (and that I believe is connected to the pressure relieve valve) and is not leaking significantly.

Finally, I tried the waste condensation pipe (had to cut it to check) with the boiler off and the pressure at 2.5 bar.

It leaked around a pint of water in three hours.

Well I think your fault is worse than mine and your problem solving seem far more proficient than mine. Me, I'd think it was time to get a tradesperson, this is not the time of year to have heating and hot water fail?

[Mike4]

Reading around, I understand that this may indicate that there is a leak in the heat exchanger.

May indicate? Its a racing certainty!

There is nothing else I can think it can be. What make and model of boiler is this?

[merluzzo]

Hi Mike,

it is a Worcester/British Gas RD 542i, at least 9 years old, perhaps more (it was in the house when we bought it)