Temperature trouble with new thermostatic bath/shower mixer tap

plumb1_2

Always problems with these cheap thermostat shower taps.
You could have higher pressure/flow rate on the cold than the hot. another issue you have is the boiler being a good distance away, so drawing a lot of cold water before it becomes hot, plus with it being a conversion the could be sections of 22mm pipe, mixing with the 15 mm outlet from the boiler.
Are there Nrv on the tap or pipes, , you might need Prv,s on the feeds to equalise the feeds.

They plumber can adjust the temp on the tap, allowing more hot to get through.
Try turning on the hot tap in the whb until it gets hot thus allowing water from the boiler to reach the bathroom quicker before turning on the bath shower mixer.
My tip is always use Mira.

sourpuss2021

Thanks, everyone!  I will do some tests and take some photos now and post them here.

By the way this tap wasn't even cheap, it was £199 from a plumber's merchants + another £79 for the shower and rail.  

sourpuss2021

Bendy_House said:

sourpuss2021 said:

Thanks, both!   Plumber had a long day because he also had to replace some floorboards and drywall after getting the old bath out, so may not have checked everything exhaustively.   Yes I think removal would involve taking the bath panel off.   I'll take another look this evening and post again. He needs to come back to put the shower screen on anyway since he didn't have time for that either.

Apart from the temperature I have been quite enjoying not having a shower screen or curtain when I use this above-bath shower.  It's surprising how little actually splashes on the floor and how much better the room ventilates.  But I digress...

A wee test. Run the shower in whatever manner it takes to run hot, and feel both sides of the mixer to judge what side the hot supply is coming from.
Laugh loudly if it's on the right.

The left-hand side is cold, the right-hand side is hot, when I have hot water flowing and press my hand to the top base of the tap.

So... that's bad? The plumber did the hot and cold connections the wrong way round?

plumb1_2

You might have reversed connections, get a small mirror sometimes there will be a red dot on the back of the valve to indicate the hot side.
tell us make and model 

sourpuss2021

Thanks plumb1_2.   Yes there's a red dot at the back.  It's on the left hand side, which is the side that's cold to touch!  

Also I took photos of all the different dial positions and whether it was hot or cold.  Then I tried them again and the positions that had been producing just hot, were now just cold. It was only producing cold water.  The heating was off at the time in case that makes a difference.

Also I'd been ignoring the boiler but actually the green light is blinking and it's flashing 00:00.  It's a Vokera.  So that's an error with it:

"Flashing Green Light

A constant green light on your Vokèra boiler is a sign that the flame within the boiler is working, and that’s what you want to see. Should the green light start flashing, that’s when there could be an issue to worry about:

    Faulty hot water sensor

    Boiler in standby"

So hopefully this is all explained by the plumber  getting the hot and cold connections the wrong way round?

sourpuss2021

I haven't been able to identify the model number of the taps, it might be on the part that's under the bath.  I could find out from the shop though. 

Bendy_House

sourpuss2021 said:

The left-hand side is cold, the right-hand side is hot, when I have hot water flowing and press my hand to the top base of the tap. So... that's bad? The plumber did the hot and cold connections the wrong way round?

:-) Almost certainly your issue.

Very likely the old taps were also plumbed 'incorrectly', and the plumber just assumed they were the right way around. Can you recall if this was the case - ie 'hot' on the RH side? How are your basin taps laid out - most likely these will be the same?

The great news is that it's a 2 minute job to undo these two nuts and turn the mixer around. The bad news is that will then mean the bath spout will fire a jet of water up in the air.

So, it's an under-bath job, but straight-forward.

If this is the cause - and most likely it is - then it'll be a toughie as to how much the plumber will/should charge you. They're the 'pro', and should have been aware of this, but it's so rare that they likely just 'assumed'.

As said by others, tho', they really should have checked the correct operation of the shower...

Let us know what they find, and how they respond :-)

sourpuss2021

Thanks, Bendy_House.   Yes if I remember correctly I think the right-hand tap was the hot one previously, though they weren't thermostatic so I never noticed.  The basin meanwhile is the correct way round but that sink was replaced a few years ago.

 

The plumber is coming back on Monday, I can manage till then.  I can find a couple of other things for him to do like blast the slow-draining basin, where the long horizontal waste pipe that connects to the main soil pipe outside the window always gets clogged up with my stubble and shaving foam!  And adjust the back panel of the bath which he didn't fully slot in previously either.  Then hopefully he'll charge me for £60 or so, but we'll see.

Thanks a lot for your help!

Bendy_House

It would, of course, have been a bit more work at the time to swap the two pipes around, but a lot less than having to go back to it now. So hopefully he'll be contrite and thoughtful in what he charges you - it was his 'error', tho' - cough - we've all done it... :-(.

sourpuss2021

Bendy_House said:

It would, of course, have been a bit more work at the time to swap the two pipes around, but a lot less than having to go back to it now. So hopefully he'll be contrite and thoughtful in what he charges you - it was his 'error', tho' - cough - we've all done it... :-(.

True!  Though to be fair it wasn't straightforward because he had to replace a few floorboards under the bath and also the dryboard between brim and floor, as there had been a very historic leak that had never been patched up.  I supplied everything he needed but did seem like quite hard work. 

He was here 7 1/2 hours and charged £380, which I'm guessing is average-to-cheap for south London.