Pump for Bath Mixer with low flow rate?

[DIY Bob]

I've just replaced my bath and bath mixer with hand shower attachment. The hot water is gravity fed with low pressure (about 2 metres head), the cold is mains fed. The hot water flow rate is about 4 litres a minute, so it's too slow for a bath! Is in possible to fit a pump on the hot water feed to the bath?

 

[PlumbBobBob]

yes it is possible. single impeller type is designed for this

 

[DIY Bob]

Thanks, Steve. Any particular recommendations? I've been looking at the Grunfos Watermill or a Supergen or similar. I could do with one that is relatively small in size...

 

[PlumbBobBob]

stuart turner or salamander are good makes. when you say you want a small sized pump, you aren't thinking of putting it under the bath are you?

 

[DIY Bob]

Well, yes, I was hoping to...

 

[DIY Bob]

Eg Grunfos Watermill Danube low voltage 1.4 bar single impellor?

 

[PlumbBobBob]

no should be fitted at base of hot cylinder. not ideal under bath because they need air circulation for cooling

 

[DIY Bob]

Thanks Steve. Looks like I've got a bit more work to do then - I don't want to boost the hot water all over the house, so I guess I'll have to run in a new HW feed from the airing cupboard.

 

[Jonwells]

Fit a 2bar single impeller salamander in airing cupboard, fit Wessex flange on cylinder, but you will need an 1 inch top (draw off) connection on cylinder for best results, pumps over 2 bar can be noisey, down load pump instructions off the net before you fit the pump, because if you don't follow manufactures instructions your boosted hot water will give you nightmares, plus if you call pump manufacturer out and it's not fitted correctly, they will void warranty or charge you to repair.
Make sure you can meet all the requirements before you purchase the pump. jon

 

[DIY Bob]

Thanks Jon. The job keeps growing. I didn't foresee this - the old bath mixer filled the bath fine, I thought the new one would do too. Should have tried it properly before finishing the bathroom - any brownie points I've earned with my wife are about to disappear...

 

[PlumbBobBob]

perhaps cheaper to get new set of taps suitable for low pressure thus securing your brownie points

 

[Plumbstar Tom]

yes, some bath taps are more restrictive than others and high pressure ones are amongst the most restrictive as are cheap unbranded ones that come in on a big ship from Chinaland

 

[DIY Bob]

Thanks guys. I can see from other threads that this is not an uncommon problem.

You're right - the ceramic mixer was a (not very) cheap B&Q model. Unfortunately, I bought a matching mixer shower and basin mixer at the same time, so to change one means to change the lot, another £700 or so. The mixer shower is not a problem, as I already have a dedicated shower pump for that. The basin mixer is slow, but just about acceptable. I also have a ceramic mixer in the kitchen and downstairs cloakroom, but the extra head makes them just about acceptable too, about 6 litres a minute. The bath mixer is the main issue - the hot fills at around 4 litres a minute, absolutely hopeless.

I was originally thinking of fitting a 1.4 bar single impellor low voltage pump under the bath, just to boost the hot water to the bath mixer. However, on thinking about it, I reckon if someone opened a hot tap in the bathroom basin or ensuite basin while the bath pump was running, there's a good chance it would suck in air...

So I'm now thinking of fitting a single impellor pump to the whole of the domestic hot water, fitting it in the main 22mm outlet pipework low down in the airing cupboard. The cylinder already has a surrey flange, but unfortunately the take-off has been used for the power shower in the en-suite. I don't really fancy fitting a wessex flange, so I might give it a go with the existing pipework first. The pump will be a good 1.5 metres below the top of the cylinder (a large one on a platform) and about 3 metres below the top of the storage tank / vent, so with fingers crossed I'm hoping I don't get air problems...

Any thoughts on a suitable pump? Jon suggested a 2 bar.

Regards, Bob.

 

[Plumbstar Tom]

is the bath filler from B and Q marked as suitable for low pressure? ie does it have a minimum pressure

if it does that it is failing as it should give a lot more than 4lpm

 

[DIY Bob]

It's a B&Q Fusion bath filler. The box says it's 0.5 bar minimum - unfortunately this wasn't mentioned on the display and I didn't notice until after I'd fitted it - an elementary DIY mistake I'm afraid. I've also had to fit 1 metre flexies as the tap position is central on the side of the bath against the wall. They don't help! I have considered taking the bath out and trying to fit solid plumbing tails that I can connect to when I put the bath back, but (a) the tiles have got to come off the wall again, (b) more brownie points lost, and (c) I might still be left with a slow bath.

If I pump all the domestic hot water, I might win some brownies back by improving the flow to the kitchen, and I'd be able to use ceramic taps when I do up the en-suite too.

 

[DIY Bob]

Success, brownie points restored. I fitted a Stuart Turner Monsoon 2 bar pump on the floor in the airing cupboard and now have good HW pressure all over the house. The bath now flows at 12 litres a minute (without changing the flexies), the mixer (with NRVs) works well, the pump was easy to fit (push fit flexible couplings) and is quiet. Much better than my original idea of fitting a pump under the bath...

Thanks to all for advice and comments.

 

[PlumbBobBob]

well done mate