Baxi 105e boiler problem?

[electricgraham]

Hi all, i,m a spark from the Electrical Forum and after a bit of help!!!!!!!!!!!!

i have a Baxi Combi Instant 105e and having a spot of bother with heating side, works fine for hot water but doesnt always switch heating on with timer but sometimes does? if it doesnt come on if i run hot tap and boiler fires up heating will then come on.
Had a Gas safe bod look at it and he just shrugged his shoulders and said it could be this or that and to start by changing X and then Y and so on? Alarm bells rang regarding cost so if any one could piont me in the right direction that would be great.

Many thanks

Graham

 

[ferret]

it dont sound like a timer problem , i,d start with the ch microswitch located at the diverter valve , check the push rod comes out and makes the switch in htg mode if not it will be the diaphram , then check the diverter valve head is operating next

 

[aggis]

Does the heating light, light when clock calls if not,
Start by making sure it isn't the clock.
If the heating hasn't come on as timed, flick the clock switch to constant,[ I ] If fires up it looks like the clock.

If it doesn't, does ? Pump run, then heating flow switch operate micro switch, then fan which makes air pressure switch followed by ignition & gasvalve. Where in this sequence does it breakdown?