No hot water - new ensuite shower

20 Aug 2017
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United Kingdom
I see this issue is not a new one, but I have a variable that I wanted to check with you guys before I do anything.

I've just moved into a house share, and the room has an en suite shower that has apparently never worked. There is a very slow trickle with the mixer turned to hot, and sometimes, if I'm lucky, if I suck really hard on the hand shower hose, I can get it to start, and then have a normal shower, but I rarely succeed with this. This certainly points to an issue with the mixer, but is this a fault on the mixer, or just a high pressure mixer that can't be used with the low pressure hot water supply? Are these mixers adjustable? I can't tell you what brand it is, because it doesn't have anything printed on it and wanted to get some guidance before I started knocking holes in the wall.

The cold water supply is at mains pressure, and the hot water has a header tank in the loft. The top of the header tank is about 4m from the mixer, so would have roughly 0.4 bar. We do know that the cylinder is somewhat silted up and needs replacing anyway, but I have my doubts that replacing the cylinder alone will fix the problem.

What would you suggest as the next steps? Remove the mixer and see if I can see a problem with it and possibly replace it with a low pressure version, or fit a pump? Or both?

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needs fitting properly, the cold and hot supplies must come from the same source i.e the CW cistern in the loft that supplies the HW cylinder must also supply the cold inlet at the shower, if you have a combi boiler then the cold inlet to the shower can be from mains
As Ian said, you need plumbing from the same source (balanced supplies), you have unbalanced supplies. I take it that you mean the shower is cold mains? If that’s the case then it’s the cold forcing the hot out of the way. A lot of showers require a minimum pressure to operate and you could have one with needing say 0.5 bar pressure. The distance needs to be the base of your cold water tank to your shower head.
Right - thank you. I get that. The strange thing here is that when I'm able to suck on the hand shower hose and get it to start flowing, the shower works fine. So I turn it all the way to hot and turn on the tap, and nothing flows. I suck like mad on the hand shower, and once it starts flowing, I can adjust the temperature with the thermostat and it behaves the way I would expect. I've had situations with unbalanced supplies before, and they manifested very differently, with the shower hardly working once the flow has started, because the cold water pressure pushes the hot water back up the pipe. This is different. There is no hot flow to begin with, but if I'm able to get ANY flow from the hot water, the thermostat does keep a decent flow at a constant temperature.

The flow throughout the house is quite slow generally, so I'm wondering if it wouldn't be worth fitting a pump regardless, and then replacing the mixer if it still causes a problem (I strongly suspect it's just faulty). In doing so, we'd want a pump that could provide pressure for the entire house, so I'd want to put the pump in line right after the outlet of the (vented) cylinder. I understand that an unvented cylinder or combi would be ideal here, but we can't afford that right now. If I were to fit a pump, what setup would you recommend? Should I:
  • Add a single channel pump on the hot water line to bring the hot water supply up the same pressure as the cold water?
  • Add a dual channel pump on both the hot and cold water, so they're better balanced? My concern here is that if someone turns on a hot tap only, the cold pump will still be running but won't have any flow.
  • Add two single channel pumps for hot and cold water, so hot and cold pressure can be controlled separately?
  • If I need to add a pump for cold water as well, can I put that in line with the mains, or should I redirect the cold water supply to come from the header tank?
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Sounds like it could be an airlock somewhere or possibly low water in cold water storage cistern in the loft/tank cupboard.

I’m not up on pumps so maybe someone else can chime in?
you cant put a pump on a cold water main, if you want tuse a pump you will have to take the cold feed from the cistern
I've bought a pressure meter and taken some readings, so I've got some more details now. The downstairs bathroom, where the shower isn't working, reads 4 bar on the cold and 0.4 bar on the hot. The upstairs bathroom, where both hot and cold barely run, don't even register on the meter. Going by distance to the header tank, I'd say around 0.2 bar. So the cold water supply downstairs is directly off the mains, and is coming off the header tank upstairs.

The easiest would be to fit a pump to deliver 4 bar on the hot water outlet from the cylinder, and on the cold water supply to the upstairs bathroom, but I'm guessing that's one hell of a pump! The alternative would be to redirect the cold water feed for the downstairs bathroom to come off the header tank and fit a more modest 1.5 bar pump, but I'm not sure I can do this without it becoming a major operation, which would end up more expensive than just fitting a combi boiler.
I’m not sure if you can get it down as low as the hot, but maybe a pressure reducing valve on cold? 0.4 bar seems quite low for that distance, perhaps you need the services of a plumber?

1m = roughly 0.1 bar pressure
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