Different water-pressures for combi-fed showers and electric showers?

EddyB

Can modern shower mixer-units taking water from a combi-boiler and electric-shower units taking water from a cold-water pipe both operate well when being fed water of the same pressure? Or do they each require different pressures?

We had a plumber round the other night to ask him to quote for fixing our electric-shower unit. The problem is that heater in the shower-unit (attached to the wall in the shower cubicle) clicks off after just a couple of minutes and then runs cold. If we leave it running (while standing there shivering with cold), then after a few minutes it will provide hot water again.

Not being plumbers or people with any knowledge of electric showers, we had assumed that the thermostat in the electric shower-unit had gone. The plumber says you can't replace the thermostat in these modern electric shower-units and that he'll need to purchase a complete new electric-shower unit to fit. He estimated a charge of roughly £130 (for the new unit) plus labour plus VAT.

But since then it's occurred to us that MAYBE the unit doesn't need replacing at all.

In addition to this electric-shower (in a small shower-room), there's a separate shower in the main bathroom. That shower was fitted a few years ago and it takes its hot water from the gas-fired combi-boiler, downstairs. But after this shower was fitted we found the brand new mixer-unit wouldn't work properly. The manufacturers advised that the water-pressure to the unit was probably not right. So the plumber came round, measured the pressure, found it was too high for the unit, and so fitted a small unit on the mains-water pipe where the pipe enters the house, and this reduced the water-pressure to the whole house. The result was that the shower mixer-unit in the main bathroom then worked properly.

So you know what I'm wondering! Is it possible that when the water-pressure to the whole house was lowered in order to enable the mixer-unit in the main bathroom to work, the electric-shower in the other part of the house was deprived of the pressure that it needs? If so, then maybe we need to solve our electric-shower problem in a different way.

Maybe the electric shower needs a pressure-pump, to supply it with a higher pressure of cold water?

Or maybe there are electric shower-units that work on low water pressures?

Or maybe we could just remember visit the water-pressure valve on the mains-water pipe and adjust it according to which of the two showers is about to be used?

There's still time for us to put a stop to the plumber purchasing a new electric shower-unit and turning up in the hope that just fitting it will solve the problem.

Any help will be much appreciated.

Thank you.

googler

If the pressure to an electric shower is too low, it should trigger a low pressure warning light. Every electric shower I've seen has one.

It is possible to dismantle and replace parts on electric showers, I replaced the solenoid on ours and gained another three years out of it prior to renewing the whole bathroom. Plumbers will tell you this is impossible when what they really mean is that they don't know how, and don't know where to source individual parts. Google 'shower doctor' to find a site that supplies them for many makes.

Your electric shower is designed to work at mains pressure, it will be connected to mains pipe work, and pumping mains pipes is forbidden. The pressure reduction should have been made on the branch to the other shower, not to the whole house.

Did the electric shower show these symptoms before the pressure reducer was fitted?

baribil

I have two showers, one electric (Triton) and one mixer (Mira), both work OK. The house supply is 4 bar (60 psi) and is not reduced at the house inlet. However, the mixer shower has isolation valves (simple screwdriver operated 15 mm) on both the cold and hot (gas combi) supplies. I have turned down the isolation valve on the hot pipe to get a better pressure balance between hot and cold during shower operation (the pressure will be the same when switched off). This mixer shower works on pressure balance within the mixer (no thermostat) - a diaphragm moves when someone turns on a tap somewhere else to rebalance. The mixer shower works better than the Triton electric shower which is limited by its heater (9.4 Kw) but has worked consistently for over 10 years. I previously had another Triton shower for over 15 years with one heater replacement - this was only discarded to get a better shower experience with the Mira mixer. I agree with a previous responder that your plumber should not have reduced pressure to the whole house but I doubt that that is causing your problem. If you want to prove it you would have to reinstate house mains pressure and reduce pressure at your combi supplied shower.

EddyB

Thanks for your help!

Yes, it would have been better if pressure-reducing valves had been added to the hot and cold water pipes feeding the mixer-unit of the
main shower. But I seem to remember it was discovered that the pipes to the bathroom shower were not accessible. Hence just one valve going on at the point where the mains-water enters the house.

We hardly use the shower with the electric-shower unit, so I only have a feeling that its clicking off is a problem that has developed since the water pressure was reduced.

The high pressure we used to have was very helpful in the garden and for maintenance tasks. But it was extraordinarily high and lots of neighbouring properties have had reducing valves fitted too.

Anyway, thanks to you, I have now tracked down the required pressures for both units, as in the instruction booklets for each. They're as follows:

Gainsborough 10.5, electric shower unit
The required running pressure is:-
Maximum 1.0MPa (10 Bar)
Minimum 0.09MPa (0.9 Bar)
at a flow rate of 8 litres per minute

Bristan Artisan Thermostatic Shower Valve:
The required running pressure is:-
Max 5 bar
Min. 0.1 bar

There isn't a big difference in the minimums, but the electric-shower does have a higher minimum than the mixer-unit working off the combi, so I think the next thing for me to do is to get into that difficult little space at floor-level in a corner of the living-room and turn up the water-pressure to the whole house to see if that improves the performance of the electric-shower! I'll let you know!

EddyB

Update: I adjusted the water pressure to the house so that it would be raised for the electric shower but still not be too high for the thermostatic mixer-unit running off the combi-boiler, and unfortunately it made no difference. So there's some other, unidentified, problem in the electric shower, causing it to shut-off in order to cool-down. I thought it would be worth checking its filter, but only one of the two metal screws holding the plastic filter into its plastic surround will come out! The other screw simply will not budge! Will ask the plumber to try to dislodge it and check the filter before replacing the entire electric shower, but if he can't, then I'm at his mercy, and about £150 will just have to be paid.

southcoastrgi

If you adjusted the main incoming stop tap you did nothing to alter the pressure at all

Stevefromdonny

Just worth mentioning, it sounds like you have removed the cover from the shower. I'm guessing none of the wires there are burnt. Electric showers are prone to burning cables, which CAN cause the problem you describe and WONT be detected by any overload device.

It is well worth opening the shower switch up and checking that for burnt cables too. Over time, with the terminals warming up and cooling down, the screws can work loose and cause the cables to burn up. They can then "make and break" their poor connection as they heat and cool.

A fuse, MCB or RCD will not detect this fault as there is no current leakage and the shower is pulling no more load than normal.

EddyB

southcoastrgi wrote: »

If you adjusted the main incoming stop tap you did nothing to alter the pressure at all

I said I adjusted the water pressure. That's quite different from adjusting the mains-water tap.

EddyB

Thanks for that. Yes, the unit is currently open, but, no, no sign of any burning anywhere.

Rang the manufacturer today and the person I spoke to said it sounds like the "thermal trip" is tripping because the hot water can't get away quickly enough. But there's absolutely no obstruction in the hose or the shower-head. So given that we've had a lot of muck in the water-supply to this region in past months I think there's a possibility that the problem could be that not enough water is getting past a blockage and into the heater, despite the pressure at the mains being within the required bars.

I told them it's impossible to remove the filter because one of the screws just won't budge and they said I should drill the screw out! But that would damage the thread and those two screws have to keep the filter unit water-tight! So, will invite the plumber to have a go at removing the screw without wrecking the seal! I'll be amazed if he can manage it.

Stevefromdonny wrote: »

Just worth mentioning, it sounds like you have removed the cover from the shower. I'm guessing none of the wires there are burnt. Electric showers are prone to burning cables, which CAN cause the problem you describe and WONT be detected by any overload device.

It is well worth opening the shower switch up and checking that for burnt cables too. Over time, with the terminals warming up and cooling down, the screws can work loose and cause the cables to burn up. They can then "make and break" their poor connection as they heat and cool.

A fuse, MCB or RCD will not detect this fault as there is no current leakage and the shower is pulling no more load than normal.

googler

If you do drill the screw out, and hence need a whole new filter unit, go to showerdoctor for a replacement.

Stevefromdonny

When you run the shower cool (ie maximum water flow, heater still on) does the water come out quite hard? If so, you probably dont have a blockage and may well indicate an electrical fault.

If you can't find an obvious fault with the shower as it is (after checking the electrics as above) I would be inclined to replace the shower. They are notoriously hard to diagnose and repair.