What's up with my combi boiler ?

[brewman]

Baxi combi 105 HE installed July 2006

It had a new fan fitted 2 months ago as the hot water would only work sometimes, that seemed to fix it but now when running the bath the water just say gets hot enough, yet downstairs the water can at times run scolding hot. After reading some other similar posts I tried turning the bath tap only half way and the water came out red hot and for some reason it turned the bath water cloudy for a short while !

Any ideas to the problem would be great

I have a breakdown insurance that I have to pay a £100 excess

 

[Billy Bob Bob]

need to ring your insurer thats what you pay them for,cloudy waters normal with very hot water

 

[brewman]

need to ring your insurer thats what you pay them for,cloudy waters normal with very hot water

I was just wondering if it could be repaired for less than £100 if I arranged an engineer myself

 

[Masood]

Bath taps have a greater flow rate than sink taps. You turning the bath tap on only half way reduced the flow rate and hey presto, hotter water. Perfectly normal.

 

[Ray Stafford]

Hi Brewman

I think this may simply be the physics of how combi boilers work.

With any instantaneous heater, there is a trade off between flow-rate and temperature rise. For example, a 24kw combi will raise approx 9.5 litres of water by 35 degrees C, or 19 litres of water by 17.5 degrees C, or any other mathematical combination.

Most householders understand this, but there are two things that they miss. Firstly, a bath tap and a sink tap which appear to be running at approx the same rate, actually aren't. If you measure it, the flow rate of 3/4" bath taps is up to double that of 1/2" basin or sink taps.

Secondly, the temperature quoted earlier is a temperature RISE, not an absolute temperature. In the summer, the incoming cold main temperature will be significantly higher than it is at the moment. So once raised by 35 degrees, it may feel hot in the summer, but only lukewarm in the winter, when the incoming main temp is barely above zero.

These two factors taken together, particularly for people who are accustomed to stored hot water, probably cause more unnecessary call-outs to heating engineers than any other factor.

 

[Leo21]

Perfectly normal, as you were.

 

[GrahamM]

As above and your cloudy water is the result of carbon dioxide bubbles produced from hot water hitting the atmosphere. Run into a clear glass and you will see the cloudy water turn clear as bubbles dissipate.
Perfectly normal!