Replacement for old high output combi boiler

[David C. Partridge]

I'm looking to replace an ageing (1986 vintage) e.l.m. leblanc GLM 5.32 combination boiler (conventional flue).

Both CH and DHW are 37.2kW (128000 btu/hr) net. DHW is fully modulating, CH modulates to low as it reaches running temperature.

Amazingly for such an old boiler efficiency is quoted at 86%!

Flow rate is fine for a shower. Our large bath takes a long time to fill. If a second tap is turned on it's a bit of a disaster (especially for the person under the shower).

I'm considering two options:

a) replacing it with a new combi with a HIGHER DHW output

b) going for system boiler with a heat store or sealed system hot water tank. However the DHW store or tank can ONLY go in the loft so pipe runs and control wiring could get a bit tricky. I'm also concerned about the economics of keeping this hot 24/7 (we can't predict DHW use well enough to cope with the "on twice" syndrome).

I'm currently leaning (strongly) to the first option, but I do realise that the second would give better DHW flow.

I've looked at some of the modern combis, but can't find any that can match this leblanc which does 16ltr/min for a 35K rise (though a few models from Vaillant seem to get close). I don't have the space to install two smaller ones, and would worry a lot about finding an engineer with the skills to do this right anyway (I could research it and DIM, but don't have the time or the Corgi certification).

Leblanc have withdrawn from UK and no longer make any high output boilers anyway.

So what are the recommendations.

Thanks Dave

[andrewpreece]

Slightly off beam here, but would fitting restrictors to the hot-water taps help out? I have no experience on this but read about it somewhere, possibly on the diyfaq. ISTR that it was suggested that people turned on the hot water tap more than they needed, and restrictors minimised the impact of a second hw tap being turned on on the shower. Is your shower a thermostatic type btw? Just wondering if you have the old-fashioned type where you balance the hot and cold water manually and are then vulnerable to taps or toilets being used.

Finally, what about the newer combis with a built in hot water reservoir? ISTR that you can get them with 11 litres or so stored away - would this feature eliminate the second hot tap problem ( as long as the second tap didn't use up all those 11 litres )?

Just some disconnected thoughts to toy with,

Andy.

[Steven Briggs]

Search the sedbuk database,

There's a "Condensa 50 Maxi" gas combi rated at 48kW, and few rated in the mid 30's. Should be enough for anyone!

[Ed Sirett]

I take it you got the figure of 86% from the rating plate on the boiler, this manufacturer seems to have no boilers listed in the SEDBUK database.

I'm fairly sure that the sedbuk figure if it were available would be a lot lower.

There are probably some combined thermal storage combis which can give very good flow rates until their energy store is depleted. These are in one unit although the most capacious are proabably floor standing and large.

Modern HW cylinders of all types are very well insulated so if you want to go the route of using a HW cylinder you won't necessarily find it takes a lot of gas to keep the store warm.