Baxi Combi 80e...is this normal operation?

[daKlone]

Hi All,

Can anyone confirm if the following is normal operation for a Baxi Combi 80e please?

When I run the hot tap the DHW circuit works as expected, but if I also run the cold tap at the same time the diverter valve pin goes in and off goes the DHW.

is that normal/correct?

Thanks

 

[cross thread]

Only if your water pressure/ flow is poor

 

[ianmcd]

Nope not normal, you have a fault

 

[daKlone]

Thanks chaps.

I have also noticed that if I turn on the COLD tap full-bore (without the hot being on), when I then turn it off the diverter valve pin comes out briefly and then goes back in.

Any suggestions as to how to diagnose the problem?

 

[gas112]

Do you have good water pressure ?

 

[daKlone]

Just measured the following:

Nearest tap to the boiler (downstairs, right next to it) = 14.8 l/m cold and 10.6 l/m hot
Kitchen tap (upstairs from the boiler) = 8.9 l/m cold and 6.3 l/m hot

Does that sound normal?

 

[Johntheo5]

Are these two separate taps a mixer with separate taps, if you turn both on, can you measure the flowrates from each? if not if you turn the hot on upstairs and the cold downstairs, can you measure these two flows, this assumes only cold water flowing through the HW tap upstairs.

 

[daKlone]

The downstairs tap is a mixer with separate hot and cold taps, the upstairs is a mixer.

To do the tests I used the individual taps downstairs and pushed to full cold or full hot as appropriate.

There was only ever one tap on at a time.

Would it be worth doing any other tests?

 

[Johntheo5]

Can you turn the upstairs cold fully on and the downstairs hot fully on and measure both flowrates, check if HW flows/keepos flowing from hot tap.
Then do in reverse, u/stairs hot full on and d/stairs colf full on.

If both the hot & cold in either u/stairs or d/stairs are on does the HW still run cold?.

 

[daKlone]

OK, so here's what I got:

Upstairs hot full on (with downstairs cold full on) = 3.61 l/m (did not heat up)
Upstairs cold full on (with downstairs hot full on) = 7.27 l/m

Downstairs hot full on (with upstairs cold full on) = 8.51 l/m (did heat up)
Downstairs cold full on (with upstairs hot full on) = 13.39 l/m

Nearest I could do with the upstairs mixer is set it to 50/50 full, which resulted in no hot water.

Downstairs I could turn both taps on full, and there was still hot water.

Does that point to anything specific?

 

[gas112]

Personally i would be stripping out the venturi and probably discover that it has fell apart and needs changing at same time i would change the diaphragm

 

[daKlone]

Had both out already. Diaphragm is not that old and looks fine, venturi looked old but OK.

 

[Johntheo5]

It does seem associated with a lower flow, you could just run the hot only downstairs and keep reducing the flowrate very gradually until the HW goes cold and then measure this flowrate, the flowswitch probably operates at 2.0/2.5LPM so if the HW turns cold at > 3/3.5LPM then maybe worth renewing both the diapragm and the venturi.
If the d/stairs tap does flow hot at < 3.0LPM then maybe some xover occuring in the single lever u/stairs mixer?.

Edit: ensure DHW temp control turned to max when carrying out above test.

 

[Johntheo5]

If its a baxi 80ECO then its minimum output is 9.3kw which means the HW temp (from mains at a now 20C) will be 57C at a flowrate of 3.61LPM so temp control should be at max or near it to avoid o/temp burner trip.

 

[gas112]

Had both out already. Diaphragm is not that old and looks fine, venturi looked old but OK.

Had both out already. Diaphragm is not that old and looks fine, venturi looked old but OK.

venturi looked like this ?