It should be just fine with 15mm. Don't reuse the 22mm HWC feed. You are
relying on this to give excellent flow, so you don't suck out the vent pipe.
If this does happen anyway, you'll need to install a flange on the cylinder.
15mm has the advantage that the hot water will come through sooner.
cope with mains pressure water, often over 6 bar. A pump will not trouble
You may need a flange. It will be much easier to install without and only
insert one if problems are found in testing. If you have a short run of 22mm
pipe from a tank directly above the cylinder without excessive elbows, or
bore reducing valves, you will probably be OK.
The output from the HWC is 22mm, rises gradually at a shallow angle and then
T's into the open vent, which drops down to the bottom of the HWC at floor
level. I can easily T into the 22mm hot supply at floor level before it
drops down to 15mm, Will it be ok to T off with 15mm pipe and use the cold
supply which is 15mm, will the differential in the initial pipe diameters
cause any problems ?
often over 6 bar. A pump will not trouble
The cold tank is above approx 6' above the top of the HWC, probably a couple
og elbows in the feed
I've also discovered one of the hot 15mm pipes in the airing cupboard only
supplies the shower so I can boost only the shower rather then all the hot
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I've recently installed a QTech 2.3-bar twin-ended pump in precisely
the same location, and am using it to supply all the hot water outlets
in the house. The flow from the kitchen tap is excellent (long run of
15mm and a continental narrow-bore tap).
I disconnected the hot supply to the washing machine as I didn't want
the pump starting every time the WM called for water. In any case,
unless I drew off a lot of water before turning on the machine, no hot
water actually made it to the machine before the inlet valves slammed
The burb that came with my pump said that if there were *more* than 3
single-use (i.e. non-mixer, or mixers connected to hot pumped and cold
mains) taps on the network a by-pass kit should be fitted. This
consists of a bit of bridging pipework connecting both ends of the
pump so that when only one end is working, there's a small flow being
pumped from the other. I have 3 single-use outlets so didn't fit (or
make) the kit.
The blurb with my pump said only use a Warix or Essex flange (not a
Surrey) as the Surrey could lead to starvation at the pump. My
plumbers' mechant thinks that's a load of old tosh, and didn't have
any Essexes anyway. So I bought a Surrey and fitted that. I also added
a supplementary 15mm feed from the cold tank to the pump's hot inlet
which should cancel out any restriction caused by the use of the
Surrey flange. The main purpose was to blend the HW down to <70c, the
max operating temperature of the pump. I bunged in a check valve too,
to stop the hot water rising by convection back up to the cold tank.
Hope whatever solution you choose works. I would have installed an
unvented cylinder but we have the prospect of buildings inspectors
poking around when our extension goes up, so that's on hold for a bit.
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