Baxi 105e Hot Water Problems - Diaphragm change?

[WesleyP]

This looks like a regular problem from what I've seen on here. Our Baxi 105e heats downstairs DHW to over 55deg C but upstairs is only about 32deg C. Very surprising as both are teed together from presumably a common outlet. The boiler is downstairs in an attached garage. From what I've seen on her the first port of call is to change a diaphragm, so I have ordered a kit part no 5111137. Are there any details available on how to change? I can't see anything in the Baxi Manual, unless it is contained in a larger assembly. Thanks

 

[Agile]

If it gives DHW to downstairs then the diaphragm is likely to be OK.

You need to turn off cold into boiler and se if any water comes out of any hot tap anywhere.

You dont get instructions on how to change simple parts because any engineer doing those jobs is expected to know how to do it.

Tony

 

[WesleyP]

Thanks, by doing that what would it prove or indicate, that cold water is somehow getting into the hot side?

 

[Agile]

I would tell me when you inform me of the result !

Tony

 

[gas4you]

If the diaphragm is just starting to perish and is weak it could possibly give the symptoms you describe.

Downstairs could be on at a greater flow rate or pressure, thus making the diaphragm operate the microswitch ok.

 

[WesleyP]

Just turned the cold water supply off to the boiler. Nothing comes out of the hot taps upstairs.

 

[Agile]

In that case measure the flow rate in litres per minute first at the kitchen tap and then upstairs.

Then repeat the measurement at the upstairs tap.

Its probably just that you have a higher flow rate upstairs and more than the boiler will heat.

It will only heat about 10 li/min at this time of year to about 46°.

But a combi is best suited to providing water at the use temperature.

Tony

 

[WesleyP]

I'm getting 12 litre/min in the bath and a temperature of no higher than 30 degc, nowhere near warm enough for a bath. I get the same at the kitchen sink, but the temp drops. Filling the sink at a slighly more reasonable rate and the temp is nearer 60. If I go back to the bath and open the hot top at a much lower rate i get almost 60, but it will take an age to fill the bath! Am I expecting too much from a combi boiler?

 

[namsag]

At 12 litres a minute you should be gettin a 35 degree temp rise so in this cold weather water will be coming in about 1 so you should be getting 36 . Could be a gas pressure problem or a sensor prob.

 

[Agile]

You could look at the FAQ on this site and do a Gas Rate to measure the boiler input power. If you have not had it competently serviced it may have drifted from its correct gas settings.

Its clear that there is not much wrong with your boiler and more to do with your expectations when the water coming into the property is cold.

Internal HW pipework should always be lagged but this is rarely done.

I have seen installations where a downstairs combi boiler is losing 3-4°C through steel HW pipes embedded in solid walls on the route to the bathroom.

Tony