Shower acting weird?

[George_A_]

Hi everyone,

I have recently entered a new property.

The property is served hot water by a gas combi boiler at a fixed temperature of 55oC.

The bathroom of the property has a shower mixer with a tap, similar to the one shown on the attached image.

From the beginning, this setup has been acting strangely.

If I run water through the shower tap, or any other tap in the house, I can mix the water by turning on the hot and the cold tap in order to adjust the water temperature to a comfortable level.

If I had water running through the shower tap and I switched the water direction to get water out of the shower hose on its own, this is where things started getting strange.

The same mixed water that used to come, say, at 37 oC out of the tap, came out of the shower hose much colder when the hose was kept at a low height and as I increased the height where I held the hose, the water temperature increased. When I moved the hose to head level (I am 6ft tall), only unbearably hot water came out of it. If I lowered the hose again, the temperature went down again.

But this was not all…

If while holding the shower hose low I connected a shower head to the shower head, only hot water came out.

I have a yearly service contract with British Gas that covers general plumbing issues, through their subsidiary, DYNO.

I called in a DYNO plumber, who came and inspected the shower and told me that the mixer had to be changed, as it was not working properly.

I agreed to that and the guy changed the shower mixer and told me everything should be fine, but he did not test his new installation before he left.

So, I am left with a brand new shower mixer with the exact same problem and some additional ones…

The shower hose that came with the new shower mixer has a much smaller bore than the old one and the shower head is also much smaller in diameter.

When I run the water through the tap, I can still mix it.

However, if I run the water through the new shower hose and shower head, turning on the hot tap makes water come out at full pressure. But when I turn on the cold water tap, suddenly the water flow coming from the shower head is massively reduced, but with only hot water still coming out of it. If I then turn the hot tap off, hot water keeps coming out of the new shower head for like one minute or so before it turns to cold.

I substituted this smaller-bore hose with my old one and the old shower head and I am facing the original problem again –water coming out of the hose increases in temperature with the height the hose is held at and connecting the shower head or partially blocking the flow of water from the shower hose makes only hot water coming through.

Does anyone have any idea what may be going wrong?

I thought I was good at physics, but I cannot think of any reasonable explanation about how the mixed water coming out of the hose is split into cold and hot water and only hot water comes out after I have connected the shower head…

Thank you in advance for your time,

Kind Regards,

George_A_

 

[picasso]

You need a couple of check valves fitted to your tap/shower, if you have check valves already they have failed and need replacing.

 

[Gasguru]

Sounds like you got a bodged combi installation...
Test the pressure from the hot and cold taps....it sounds like the cold is being fed from cistern (tank) at low pressure whereas the hot is on mains pressure.
If so then get the cold plumbed from the mains too.

 

[Madrab]

Get the Dyno guy back in, he hasn't fixed it!!

 

[dilalio]

Get the Dyno guy back in, he hasn't fixed it!!

Hmnnn... Dyno guy = drains not mains

 

[gasbusters]

How do you kniw the water is coming out at 37c?

You should fit a thermostatic bath mixer tap, 50 quid of ebay.

 

[Gasguru]

Can we establish pressures first before you go recommending Chinese carp from eBay that's unlikely to be WRAS approved.

 

[gasbusters]

Can we establish pressures first before you go recommending Chinese carp from eBay that's unlikely to be WRAS approved.

he did say he has a combi so i'm guessing the water pressure must be half decent, 0.5 bar is recommend for a lot of thermostatic shower mixers to work.

 

[Gasguru]

Yes he's got a combi but where does the cold water at the shower originate?
Plenty of cowboy installers will leave the cold bathroom supply's off an old cistern feed rather than move across to the mains. Unbalanced hot and cold causes no end of problems including a serious health hazard on occasions.

 

[George_A_]

You need a couple of check valves fitted to your tap/shower, if you have check valves already they have failed and need replacing.

Sounds like you got a bodged combi installation...
Test the pressure from the hot and cold taps....it sounds like the cold is being fed from cistern (tank) at low pressure whereas the hot is on mains pressure.
If so then get the cold plumbed from the mains too.

Can we establish pressures first before you go recommending Chinese carp from eBay that's unlikely to be WRAS approved.

Yes he's got a combi but where does the cold water at the shower originate?
Plenty of cowboy installers will leave the cold bathroom supply's off an old cistern feed rather than move across to the mains. Unbalanced hot and cold causes no end of problems including a serious health hazard on occasions.

First of all, a big thank you to everyone for your replies.

Picasso, I bought a check valve, this one (https://www.screwfix.com/p/non-return-shower-check-valve/71542?_requestid=359179) and fitted it where the shower hose meets the mixer, but it did not work.

Gasguru, I think you may have a very valid point, I can see even without a water pressure gauge that there is a difference in water pressure of hot and cold water...

The mixer has the shower hose outlet facing upwards. So, if I remove the showerhose, I can see that at maximum opening of the cold or the hot tap, the hot water reaches a much higher point shooting upwards than the cold water...

I suppose the repair may be very costly for that...

I have contacted DYNO and they are sending someone back to check it out next Wednesday or Thursday...

Kind Regards,
George

 

[picasso]

Hi George yes as soon as gasguru posted the 'penny dropped that the check valves would not help in your case, quite surprised the dyno plumber did not mention the difference in pressure as presumably he had to drain it down ?

 

[Gasguru]

Stop fannying about with pressure gauges...stick your thumb over the tap or shower outlet and compare the hot and cold pressures. If the cold is still off the cistern it's just a matter of connecting the rising cold main across to the cistern cold outlet...a 10min job. Check the WC as the float valve may require upgrading to mains.
Keep us posted.

 

[George_A_]

Hi George yes as soon as gasguru posted the 'penny dropped that the check valves would not help in your case, quite surprised the dyno plumber did not mention the difference in pressure as presumably he had to drain it down ?

Stop fannying about with pressure gauges...stick your thumb over the tap or shower outlet and compare the hot and cold pressures. If the cold is still off the cistern it's just a matter of connecting the rising cold main across to the cistern cold outlet...a 10min job. Check the WC as the float valve may require upgrading to mains.
Keep us posted.

Thank you both for your replies.

Well, Gasguru was right this time... The DYNO guy (his name was Nathan) came over and he was the first one out of 3 visiting plumbers who managed to identify the cause of the problem -and it was exactly that... Nathan told me that the plumber who installed the combi boiler must have been lazy and left the bathroom feed of cold water from the tank still found in the attic, which feeds cold water based on gravity (so, when I lifted up the hose to wash my hair, this explains the reduced cold water pressure which allowed the hot water to overtake the cold water supply). Nathan showed me the pipes in a cupboard next to the bathroom where you could clearly see that the plumber had sealed with a tap the hot water pipe that was possibly coming out of a heater placed in that cupboard, while the cold water was coming into the bathroom from a pipe above it, pointing to the fact that it is possibly coming from a cistern tank up there...). (attached is a screenshot of his report)

As this repair was not covered in their repairs terms and conditions -they consider the job as an upgrade, which is not part of the repairs contract- he quoted me for switching the cold supply from the cistern tank to the mains for £136 incl. parts and labour (attached is also a screenshot of his quotation).

If anyone in here has some experience on the issue, is that a reasonable price to charge for this job or should I try to get more price quotations?

Thanks again everyone,

Kind Regards,
George_A_

 

[Madrab]

Depends on what is required. If it's a simple cut in from one pipe to another in the same location then it's a piece of pizz, if not then it may be more complicated. I wouldn't say that's overpriced though. Nothing stopping you getting a couple of independents in and see if they can do better tho.

 

[oldbuffer]

Sounds as if you have a solution, at a cost no greater than £136. One point to consider is that when you convert all cold supplies to mains pressure, you'll need to be certain that any WCs connected to the system are properly configured for high pressure supply. Otherwise they may fail to shut off when full and run the overflow. I would expect your plumber to be aware of and prepared for this.