HELP: Baxi Boiler or Bristan Mixer at fault ?

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This summer I had a Bristan Artisan Thermostatic Bath Shower Mixer Part Number: AR THBSM C installed in a new bathroom. 0.5min to 5bar max.

The boiler in the house is Baxi 105e and is about 4-5 years old. It seems to be working fine but i have noticed that unless i set the kitchen mixer tap all the way to hot it will not sense demand easily. It's as if its not sensitive enough to demand.

The mixer shower is fitted in the bathroom just above the boiler in the kitchen. 15mm hot and cold pipes run from the boiler, through the ceiling and into the the bathroom. The 15mm pipes are than adapted to 22mm (about 50 cm length from mixer) to connect to the mixer shower.

The problem i'm having is that when i put the shower mixer on - even to highest mixer temp it does not create demand to the boiler for hot water and it remains cold. It did work ok a few months back but now it doesn't at all.

If i first run the bathroom basin mixer tap hot for few minutes than i can get hot water from shower. But this will cut out after a while & revert to cold after basin tap is off. I have noticed that even running the basin mixer tap (Bristan) at max hot it seems to take a while to get boiler demand going. But once it does it remains unlike the shower.

Do i have a problem with the cartridges in the mixer shower ?
Or can it be the thermistor in the boiler ?
Should my plumber have run longer length of 22mm pipework to mixer from boiler ?

Please advise as family is getting fed up with cold showers and the blame is falling on me : (



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most likey the diaphragm on the pressure differential has split or stretched according to the first lines of your description.
 
Is the part you are suggesting described accurately as "Baxi Combi Instant 105E HE DHW Diaphragm Kit" ?

From the fact the bathroom basin mixer occasionally suffers the same problem can I confidently eliminate the thermostatic shower mixer as the problem ?


I will get & fit the part tomorrow if available locally and let you know how I get on. Are there any other parts that might be in question that I might as well purchase in case the diaphragm doesn't fix the problem ?
 
If you have a hot tap you can measure the flow rate at which the boiler just turns on.

It should be at about 2-3 litres per minute.

Tony
 
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I was not able to source the diaphragm locally do placed on order. Hopefully will be here before Christmas.

I did another test today. I closed the cold water stop valve to the shower mixer (located next to mixer) so only hot water from mains was available.
I turned on mixer and upped temperature on thermostat to maximum and still no hot water from boiler.

I tried to check the flow rate at which the boiler just turns on but couldn't as i have mixer taps in house. I will try to get a stop valve flexi pipe connector and carry the test out soon.

In case the replacement of the diaphragm doesn't resolve problem is there anything else i should be looking at ?

-Microswitch ..Thermistor ?
-Could the thermostatic mixer have a fault ? Tried to call Bristan today but gave up after 15min in waiting queue on 08 number.



:confused:
 
Just to clarify the exact Boiler I have is the BAXI COMBI INSTANT 105e.

I failed to point out in my original post that it was the INSTANT model. Just in case it helps with diagnosing.
 
*EDIT* Additional Info That May Help Diagnose Problem

Today I noticed that when boiler is not sensing hot water demand from kitchen or bathroom taps (mixer tap full to hot), If the boiler is powered OFF and back ON it get the hot water going again.


*Update *Still waiting on the diaphragm to arrive. Hopefully make it before Christmas cut off :cry:
 

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