Hot water at the sink tap but not at the bath tap!

[happytodayhappytomorrow]

I went to run a bath last night at about 10pm (probably the time is irreverent but hey ho)

There was boiling hot water at the kitchen sink tap.
There was boiling hot water at the sink tap in the en-suite.
There was boiling hot water at the shower cubicle and the sink tap in the bathroom.
But, at the bath tap in the same bathroom, there was only tepid water.

This has been happened before but it’s certainly not always the case.

Any ideas please what could be causing this?

You've got a combi boiler, I suppose?

1. take a photo of the bath mixer please. How old is it?

2. fill a bucket at the hot bath tap. Time it. Calculate how many litres per minute it delivers.

How new is the house? If it's relatively recent there could be a mixer to limit the temperature.
Given the weather is warm, I'd expect a Combi to work better, but how often do you have a bath? Could be that turning the tap slower could produce hotter water, try that.
We have a 24kw Combi and for a bath you have to turn the tap about 2/3 on to get the fastest fill of warm enough water.

Thanks for both the replies.
The house is circa 1930s. We did a refurb/extension in 2003.
We had a new boiler fitted about 6 weeks ago but this problem has occurred with both the old and the new boiler.
The bath and taps were fitted, we think, about 17 years ago when bought the house.
Photo of bath taps attached.
Usually with the setting here just shy of 30 you get a pipping hot bath. But when the problem occurs, I can turn the setting to 50 and still only get luke warm water.

I think it's the mixer tap. I can't see it well but I presume it's thermostatic and may have an anti-scald device. There should be a button to release it, might be stuck or scaled.

but I still want to know your litres per minute.

I’ll do that now PJ. Does it matter if I use hot or cold water for the litres per minute?

Does your tap just do the bath? Or does it work as a shower control too? As PigletJohn says, it is likely to be the thermostat, especially if the tap is 17 years old. On the plus side, you should be able to order a new one to replace it and if you or your partner feel confident, you can do the job yourself.

Also he'll be looking for the litres per minute on your hot water.

yes, hot only.

11 litres of hot water in 1 minute.

Yes, there is an anti scale device but last night I clicked past it (at about 35 you have to squeeze the side of the twisting part of the control) and turned it up to 50 but still got no hot water.

There is a shower attachment too but that also only produced luke warm water last night.

Doing the measurement now, I’m getting piping hot water with the control on 25.

aha

could be that the knob or mechanism has slipped and the indicated temp no longer reaches actual temp

Can you leave the temp knob at a setting that is satisfactory, and ask people not to change it until it is replaced?

At seventeen years the mixer has probably had a good life. Unless you know the brand, repair would be tricky (some major brands offer overhaul kits)

Thanks PJ. I really appreciate your advice.

But if I’m understanding correctly, that doesn’t why it sometimes gives me piping hot water and sometimes gives me tepid water while on the same setting.

I'm guessing that the mechanism inside the mixer is not rotating in accordance with movements of the knob.

I can imagine some part has come loose or broken.

there is a faint chance there is a grubscrew on the knob that should lock it onto the spindle. These are usually very small and placed so they do not catch the eye. If present, the screw may be made of brass which is very soft so verify that your screwdriver is a perfect fit before trying to turn it. Or the spindle may attach to the knob on splines and the screw will be hidden under a button in the middle of the knob.

But I think more likely an internal fault that you will not be able to fix.

It will be due to the thermostatic cartridge reaching the end of its life. I would still say that it would be worth your while to change it if you know what make and model it is. As it's a concealed unit, it will be quite difficult/expensive to change it for a newer unit. If you do know which make and model it is, go on to the manufacturers website and you should be able to order one from there

Thank you very much both of you. DH and I will take a look in the morning.

this company are very good for parts. If you can't find yours, send them several photos from all angles

shop.lunns.net/