Bathwater not hot

[Ricky2]

Our boiler is an oil-fired Worcester Heat-slave 20/25 in a newish (7 years old) four bedroom house.

Normally it works admirably on the central heating plus all downstairs sinks and washbasins

Upstairs it works fine in the washbasins but only on one of the baths.
The other bath runs hot as long as you adjust the hot tap to a very low flow rate and add the cold water afterwards. [If you try to run the hot tap at a fast rate the water runs tepid. If you run the cold tap at the same time as the hot that also end up with a tepid bath]

Any ideas as to why please?

 

[Bahco]

Is the pipe 22mm supplying the hot tap

 

[Ricky2]

Looks more like 1/2" Bahco

 

[Bahco]

Thats how combis are I'm afraid, as they heat up the water as it passes thru the heat exchanger.

 

[JohnD]

I'd guess the hotter bath has a lower flow rate. Measure it with a bucket and a watch and see how many litres/min each gives.

I presume the "cold" bathroom doesn't have a long, uninsulated pipe under the floor or anywhere cold, does it?

 

[Ricky2]

Thanks for the comments
No John the 2 bathrooms are in fact "back to back". The en-suite bath pipework is no more than 4 feet away from the main bathroom inlet.
Sounds as if it really needed a bigger combi?

 

[JohnD]

if 20/25 if the heat output in kW, then, yes.