We've just had a WB 40 CDi combi installed into a house that was previously a standard boiler/tank/cylinder affair. The short story is that we can't run a bath and shower off it at the same time (I don't mean that the pressure drops off a bit on the shower - it actually stops). Various plumbers and even the WB site itself would indicate that you can't expect to do everything at once on a combi, but I did expect more when just two outlets were opened.
Any ideas why this might be and/or what can we do?
[big detailed description]Of course there was no existing pipework for the hot water from the boiler position, but luckily there was both a hot and a cold 15mm pipe right under it as that's where the washing machine is.
The plumber has used these (thus reversing the old hot flow - presumably the cold is the same as it always was as the washing machine would have been plumber off the mains). The 22mm pipe that used to come out of the cylinder has been capped above the airing cupboard floor (we'll be taking it into the loft later to drop down as a shower). The 15mm mains feed to the old cylinder has been spliced into the remains of the 22mm pipe from the loft tank to the taps and likewise a spur capped above the floor for the later shower. We haven't had the taps/mixers replaced as we're doing the bathrooms later this year, so the bath/shower mixers are still the old 22mm-feed ones. The plan is to have a shower in the ensuite and a both/shower in the bathroom.
The cold water pressure is excellent, even through though those bath/ shower mixers. So I can run the cold into the bath and a cold shower at a good rate for both.
The hot pressure is a lot less than expected. We did expect a drop in pressure if you were running both, but the current situation is that running the hot into the bath leads to not enough pressure to keep the shower on in the ensuite.
If I run the sink tap in the bathroom instead of the bath mixer (my attempt to simulate drawing off water through a 15mm bath pipe), we do still get some pressure out of the shower. It's reasonable, although right at the bottom of my expectations/hopes pre boiler install.
Another plumber that we've had around to quote for kitchen work expressed surprise at the flow when he saw just the bath turned on.
Any general comments would be appreciated, but I've a few specific questions (which may or may not be pertinent):
- 22mm pipes. I'm not sure as chipboard floors are preventing me easily checking, but I believe that the 15mm hot out of the boiler probably becomes a 22mm pipe under the 1st floor and then into the bath mixers. Might that be the problem?
- Length. I'm pretty sure that the cold supply to the boiler is fine as the cold tap in the cloakroom (just before the boiler in the scheme of things) belts out water. The total length of the hot supply from the boiler to the bath mixers is probably 15m+ (all on ground/ first floors). To give you an idea, the kitchen tap (which is probably closer to 20m from the boiler in pipe length) takes ~60 seconds to heat up if it hasn't been used for a whilee. Forgetting it's bore for the moment, might the length of the pipes be an issue pressure/flow rate wise?
- Kitchen tap. Whilst we're doing the kitchen, we're having the ceiling down. We thought it would make sense to run a hot feed from the boiler the ~5m to the kitchen tap, which will presumably reduce the time-till-hot to a perfectly fine 10-20 seconds. Might it also make sense to carry that 15mm feed up into the bathrooms to try to solve our pressure/flow problem?
It's worth noting that although some plumbers expressed concern at switching to a combi for the house, British Gas were quite happy to install effectively the same boiler rebadged. Presumably that wouldn't be the case if it was a total no-brainer bad idea :) .
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