Bath shower mixer confusion

[SheilaWilde]

I'm posting this in the hope that someone can give me some advice. @PigletJohn could you possibly help?

I've got a combo boiler with low pressure (that's a whole new exciting thread) and a shower over bath fed from taps. The taps are leaking to buggery and I can never get the shower to 'mix' it's either boiling or cold because once I add cold to a certain point (turning the cold tap in mm increments) the hot gives up and it goes cold.

I thought over half term I'd have a go at installing new taps - which I may or may not regret but I can't really afford a plumber at the moment. I thought I'd just buy the cheapest B&Q taps, which is what I've got (so I'm not sure why I thought going for the same thing - that's broken - was a good idea). So, looking at mixer taps on Screwfix some say good for low pressure but reviews say they don't mix. Does anyone know what I need? I found these at VP which seem to fit the bill but the description doesn't mention combi boiler. I don't want to spend £100 on something that won't be better than what I have.

Also, if I do buy taps. Is this a simple DIY job? I'm quite handy but I havn't ventured too far into plumbing DIY. My toilet is also leaking but I'll leave that excitement for another day.

These are the taps I found but I'm not sure they're what I need.

https://www.victorianplumbing.co.uk/modern-chrome-thermostatic-bath-shower-mixer-tap-slider-shower-rail-kit?campaign=googlebase&gclid=CjwKCAiA3KefBhByEiwAi2LDHADX5ucb5plNypr6GaJIco-RSSgG5oteuOfgj9012AsMI4neranvhoCeWQQAvDD_BwE&gclsrc=aw.ds

Sounds like you need to look at the boiler pressure first. Round my way the water company has turned down the pressure for the whole street to help reduce leaks in the road.

What I mean is, don't spend on taps to have the same issue. Change the washers & look at the boiler. Does it need topping up? The pressure is usually between 1 & 1.5 I think.

Thank you for replying. My water pressure has always been low and my boiler is a Worsester Bosch that's designed to work from 0.5 bar. I never get higher than 1 bar and I do top it up when needed. It's serviced every year but is a constant annoyance. All the houses in my row of houses have low pressure. I've had the water board out countless times to measure the flow rate and outside it gushes but inside it doesn't. I've had the pipes flushed and the boiler was fitted in 2018.

I need to replace the taps because they're leaking from both where the shower hose meets the taps, from the taps themselves and from the actual water inlet hose? My exDH fitted them - he's not a plumber. I thought taps were taps and didn't realise that some work better with low pressure over others. You also can't 'mix' effectively with the taps I've got whereas the ones I linked to - which is a whole new rabbit hole that I've been in - look like you can effectively mix.

The pressure in the boiler is irrelevant to the pressure in the taps.

So you have a combi boiler, so no hot water cylinder and no tanks in the loft.

Fairly odd that the cold pressure overwhelms the hot, then.

How old is the house, and the plumbing?

Fill a bucket at the bath cold tap. Time it accurately. Calculate how many litres per minute it delivers. Now do the same with the hot bath tap. How many lpm?

Put your thumb over the spout of the bathroom basin hot tap, and turn it on. Can you hold back the flow? Now the cold one.

Now measure the flow and try the pressure at the cold tap in the kitchen sink

And, if you have them, the garden tap and utility room tap.

Photos of your taps, pipes and main stopcock may help, especially of the incoming watermain, under the stopcock, which might be lead, iron, copper, black plastic or blue plastic. What diameter is it?

Thank you so much PigletJohn. I'll do the timed ppm in the morning. I just tried to do the 'hold back the flow' on bathroom sink and bath but they've got those things on that I got free from the water board that sort of dissipate the water - rather than being able to stick my finger up the tap. I managed to spray water everywhere rather than hold back the flow but if it was a 'normal' tap I think the pressure behind my thumb hand wouldn't last long. But I'll time the flow on the morning.

The house is probably around 18c, no garden tap or utility room (I wish). The pipes are probably old because I've never updated them and I've been here 14 years. The previous owners were here probably 30 odd and weren't big on doing anything that couldn't be solved with a bit of gaffer tape.

These are the lpm numbers @PigletJohn. I only had a 1 litre jug so I filled to a litre and then scaled up - hopefully correctly.

They're all very low. I think the problem is probably your pipework. Have a look at the material and diameters please. Photograph all the stopcocks and service valves you can find. I don't recommend mixer taps.

I can't see any of the pipes because they're under the floor boards. The stop cock is currently inaccessible (I know that's not a good idea) but it's a red lever and it's fully open. The boiler engineer checked it at the last service. The low water pressure has always been an issue. I live at the top of a hill, served by a secondary pumping station 4 miles away, downhill. I'm the third to last at the end of the pipe.
I know mixer shower/bath taps aren't ideal but I can't afford an electric shower so I think the b/s mixer is the only solution? Is there another solution? If not, would there be a particular mixer I should get? The thermostatic ones look like they're suited to what I need (a shower that doesn't go cold) that run on low pressure. This one runs on 0.1 bar (the maximum bar I get is 0.5) and has a flow rate of 9Lpm.

www.toolstation.com/mira-atom-deck-mounted-thermostatic-bath-shower-mixer/p70250#reviewTab

I also didn't realise the pressure in the boiler isn't related to the pressure in the taps?

The boiler is a sealed system and is 'inflated" to the correct pressure, then its filling valve is closed, and, apart from leaks, and expansion due to heat, does not change.

The pressure in the taps varies with time of day, and how many are open.

I think your water supply pipe might be a small one, put in when the house had a cold water tank in the loft, which could be filled slowly, and could deliver water to the bathtaps faster than it was topped up from the mains. This was (is) very common and is why older British bathrooms have large taps, for good flow at low pressure.

I think your problem is more likely poor flow than poor pressure, though you might have both. The thumb test gives an idea of pressure. If flow outside the house is good it may be your pipe.

My previous house had a lead water pipe of 3/8" internal diameter, and water flow improved hugely when I dug up the front garden and laid a 20mm plastic one. I realise this may not be easy. Sometimes you can improve flow by fitting larger stopcocks which are less restricting. It will be difficult to diagnose without seeing the pipes.

Thanks ever so much PigletJohn. The teenagers are home now so I'll get one of them to move the fridge so I can photograph the stop cock which should also show the pipe.

I've just been to B&Q to look at bath/shower mixer taps but no one in there could give me any advice on which ones work for poor flow and they didn't have any thermostatic ones so I'd still at square one.

I really appreciate your advice, thank you.

If you scratch the pipe you should be able to identify the material. Try to measure the external diameter.

IMO the Aqualisa round-bodied shower mixers are very good. This is a very simple but effective design they built their reputation on. Once you know the shape you will see it is different from the more complex designs. It has a cartridge with a thermostatic spiral inside, and hardly anything to go wrong. For example www.screwfix.com/p/aqualisa-aquavalve-rear-fed-concealed-chrome-thermostatic-mixer-shower/32030
Or
www.plumbworld.co.uk/aqualisa-colt-concealed-3253-23707

They make a variety of more expensive and more complex showers but I prefer the round ones.

There are (were?) some surface-mounted models but they may have been discontinued. The round ones are quite easy to service and IMO better and more reliable than bar mixers. Ebay had some on clearance from Plumbworld

Thank you. I've managed to get to the pipes.

The showers you linked to look good but I'm not sure how to fit them because my shower currently comes off of the bath taps. I assume there's a dual fitting I need to split the taps? The other issue is (the wall the shower is attached to isn't a proper wall - I made it myself - so I'm not sure it has the integrity to hold a shower all by itself. Although it's quite strong but I'd probably have to pull it apart to fit a wall shower.
I've just searched and Aqualisa do a bath/shower mixer but it seems to need a minimum pressure of 1 bar. The Mira I think I linked to works from 0.1 bar.

Most of your newer pipework looks quite good

But

In the pic with a white cloth, there is a pipe coming up from near the floor. It is darker than the others so probably the cold supply. It has a large brass fitting on it and a small chrome one. I think the chrome one is a budget ball valve. These have a small orifice inside that constricts flow. If you change it for a full-bore valve you may get an improvement in flow. It is a fairly simple job if you are fond of plumbing. I am not sure if the brass fitting is a valve or just a connector. I will post links shortly. The pipe looks like 15mm copper (about the size of your finger) which is the smallest in common use and IMO a bit small for filling a bath.

Look out for any more of the little ball valves on your pipework. They are handy but not very good.

This is an example of a very good full-bore valve
www.screwfix.com/p/pegler-ball-valve-blue-15mm/11085

This is an example of the other sort
www.screwfix.com/p/isolating-valve-15mm-10-pack/32802

You will notice that one costs ten times as much as the other. This is because it is ten times as good.

Looking at your pic down the side of the fridge, the pipe coming out of the floor is bigger than the pipe above it. It is too dark to make out what the fittings are or what the pipes are made of. It might be possible to use better fittings or a bigger pipe, or split off the hot and the cold pipes near the stopcock to reduce contention.

It might be lucky if the incoming pipe is black plastic.

As you have poor flow in the bathroom, I think you will get better results with a separate shower, and individual taps. If you photograph the taps I might be able to suggest how to renovate them.

I'm intrigued reading this!
I'm presuming the water is coming up the pipes from the ground so my question might be moot if the water is flowing downwards...
Why would they put a constricting ball valve on a pipe in which the direction of flow is upwards?

Hi @SheilaWilde I fitted the Bristan Quest taps with shower attached in the summer myself. I have a combi boiler with a shower at the other end of the bath with a just a fixed head rainfall? head. I needed something to be able to rinse the bath and my hair after colouring it. I did not want to disrupt the shower as it has been well fitted. (Not by me, I have fairly recently moved in ).
I am actually quite pleased with it, I am not saying its a super duper powerful shower but it has worked well for my needs.
Plus they are a massive improvement on my last peeling chrome spindly taps.
I did have some issues with the pipework but got there in the end.The taps were easy to fit though. I used JG flexi tails, 1 end in taps, 1 end push fit ontpo copper piping.
I bought pipe the hand round pipe cutters from Wickes for cutting the copper.

Because they weren't aware that those valves constrict flow, I expect.

@PigletJohn

Gotcha!

Just had to pop on to say PigletJohn is a legend. So generous and helpful. It's a lovely thing to see.

PigletJohn you're so tirelessly patient and kind. Thank you.
However, in my usual 'oh it can't be that difficult' way, I thought, before buying new taps, I'd just make sure I could get the old ones off. Teenager pulled out the fridge and I turned the water off. I couldn't get the taps off but instead managed to flood the bathroom. I've got water trickling into the kitchen. DS helpfully came down stairs and said 'mum, did you know the bathroom's full of water? Oh, and look, the ceiling's leaking' helpful as ever. But, before that I decided to try to mend the toilet (constantly leaking water into the bowl). The top of the cistern is now on the floor and I've tied the float/inlet thing up with string to the cupboard above so it can't fill the cistern unless you release the string. Then, just incase that wasn't enough water fuck wittery - to look at the pipes and get a photo, I emptied out the airing cupboard (the bit on the photo is the bottom and was housing a collection of paint cans and a bag of jumpers that I thought I didn't want - turns out I do and my favourite jumper - that I got from the dump was in there. Every cloud) and realised there was water dripping down the pipes from the boiler. Worcester Bosch were helpfully unhelpful and now I've got to find a plumber to look at the boiler, even though it's still under guarantee.
But. To your point about the ball valve, why would they use something that constricts the flow? I've had sooo many issues with this boiler and WB saying it's my water and it could just be a ball valve?? I'll have another look in the morning, I'm deliberately ignoring any dripping sounds - I've put a big plastic storage box under the bath to try and catch the drips.
I've told DS and DD to consider becoming plumbers.