Bath tap hot water mystery

[benito]

Can anyone please explain to me why the hot water coming out of my bath tap is only around 35 degrees, not hot enough for a bath? The other taps and the shower unit (uses boiler hot water not electrically heated) are all boiling hot. Even the sink tap in the bathroom is really hot and it's only 3 ft away.

It is a 3 year old house so there shouldn't be anything major wrong with it.

Any help or tips greatly appreciated.

 

[GreenArmy]

Do you have a combi boiler? If so, try turning your bath tap on only half way i.e reduce the flow. Try it and see what happens.

 

[benito]

Thanks for the reply. It is a combi boiler. I tried as you suggested, and it did give me really hot water for a short while, then it went really cold again. Tinkering with the speed it comes out does seem to have an effect, but it is all a little too random.

If you try to warm up bath water whilst you're in it, it teases you with some really hot, then goes cold, as if the water's not being heated properly from the boiler. The mystery is that the sink tap can be fully open and it's still piping hot.

Very confused!

 

[uug197h]

is it a mixer tap

 

[GreenArmy]

Your bath tap will be 22mm whereas your wash hand basin and kitchen sink tap will be 15mm. Now assuming your pipework to the bath hot tap is 15mm, your tap will almost definitively be 22mm.
Now my bath tap acts almost the same as yours in that if i fill the bath with the tap full bore i barely need to add any cold. This is also due to the temperature of the incoming main as its hotter in the summer. But if i reduce the hot water tap to the bath on initial filling i can get the bath really hot.
When you are in the bath and you want to top up the hot water you will always get a bit of hot, then cooler water before it gets up to temperature.
I have toyed with the idea of replacing the bath taps with 15mm basin taps but to be honest its not really much of an issue in our house.
Maybe other forum members can suggest something else? Maybe a pressure reducing valve on the main before it enters the combi?

 

[benito]

Yes, but I have to run the hot on its own as it's not hot enough to need any cold. It used to work fine, but in the last few months it has become colder and colder. It does suffer if the cold tap is on too, with the usual pressure issues.

Ah, okay. Thanks Mark. That does make sense as it is pretty chilly at the moment so the incoming mains temp would be lower. I'll try your method and see how it goes. At least I have an idea why it may be.

Thank you