Baxi 105e Combi Boiler Hot Water Startup not always happenin

[Dave1999]

Baxi 105e Combi Boiler Hot Water Startup not happening for upstairs shower and taps. I need to get it started by having shower running and then starting hot water at downstairs tap. Boiler then it fires up, I switch off downstairs tap and shower works fine. This only started recently after I had turned the water into the house off at mains. I thought the problem was because I hadn't fully opened the waters mains tap when turned back on because initially after opening fully, the upstairs hot water seemed OK, didn't last though and back to same problem next day. I assume this is a water pressure problem, but possibly caused by a fault on the Hot Water sensor/microswitch. I actually have a spare sensor/microswitch cos I had to replace the Central Heating one some years ago when the opposite was happening, the central heating didn't fire up after requesting hot water. Replacing the Central Heating sensor/microswitch fixed that. Could this be the hot water sensor/microswitch or is this a water pressure problem and if water pressure need advice how to fix? Any advice appreciated.
Dave Stewardson, Mobile 07795617859

 

[twgas]

More likely the HW diaphragm, you should only need a few litres per minute to fire boiler.

 

[Dave1999]

More likely the HW diaphragm, you should only need a few litres per minute to fire boiler.

No issues with downstairs taps in firing boiler every time, just the upstairs taps and shower. By starting shower upstairs then starting hot water tap downstairs, boiler fires up, then stop downstairs tape and hot water upstairs working fine e.g. boiler stays fired up. How would HW diaphragm problem cause these repeatable symptoms as opposed to HW microswitch problem. need to know before I decide what to do next.

 

[gas112]

The diaphragm has stretched and on its way out is most likely cause and shows up on some outlets but not others

 

[Dave1999]

More likely the HW diaphragm, you should only need a few litres per minute to fire boiler.

Replaced the diaphragm and noticed the valve was well clogged with what looked like solid chloride. Cleaned as best I could and initially didn't fire up at all, started again and then working fine for all but 1 shower, which just needs hot water started in sink in same en suite and then shower gets the hot water. Will leave as is as working consistently now for all but initial start-up of 1 shower.