Baxi 105e instant interesting problem.

[Duggie]

Hi All,
I hope you can help, My boiler has started to cycle( hot water led / fan no flame light) when i turn off the cold water tap quickly. I have removed the DHW micro switch and the pin extends when i turn off the cold water tap,Also if i make sure the pre-heat is off and leave the boiler on over night the temp indicator will stay on 30 degrees until i rest the boiler and then it goes out until i run the hot water tap and the temp increases as normal but will only come down to 30 degrees until left over night and then reset.
everything else works perfectly!

Any ideas would be welcome ( i have ordered a diaphram kit as its 5 years old and never had one)

Thanks Lee

 

[Gasman87]

a split dhw sensor diaphragm is a very common fault on these.
firstly the dhw sensor pin should not be extending when you turn the tap off as you say, try removing the dhw sensor diaphragm and inspects it for any splits.
its only a 15min job, just isolate your main (try not to ever use the boiler isolation valves as they can leak when moved), open a hot water tap to release the presure, then unscrews the 4 screws and pull it apart.
can be a bit of a fiddle putting it back together tho as you have to line the spiindle up with the hole against the pressure of the spring.

 

[aggis]

Could have a dead leg on the cold, did you have a cylinder removed & pipes capped off when boiler installed. When a pipe is capped it must be bled of air, otherwise it can cause the boiler to fire for a second or two when cold turned off.
Bleed the pipe/pipes if poss, or fit a non-return valve with an mini expansion vessel on the cold inlet to the boiler.

If not sure get a plumber

 

[Duggie]

Thanks for your help.
I think it may be the dead leg problem as when i had my bathroom done the plumber mentioned something about spare piping being left after the new boiler was fitted. will try and find this extra piping and see if i can bleed it. I take it that the highest point is the place to do this?

Thanks lee

 

[Billy Bob Bob]

Thanks for your help.
I think it may be the dead leg problem as when i had my bathroom done the plumber mentioned something about spare piping being left after the new boiler was fitted. will try and find this extra piping and see if i can bleed it. I take it that the highest point is the place to do this?

Thanks lee

or find it and cut it out

 

[Duggie]

Thanks to all that have replied, aggis you were correct just been into the airing cupboard found two pipes caped off, turned off water and bled both pipes slowly, all sorted like a new one .

Again thanks to all for your help.

Lee