baxi system 35/60 problem

[Malty]

I am having a problem with a Baxi system 35/60 and would appreciate some help.Flow switch spindle does not always come out fully to make the microswitch.This only happens when the boiler has been off overnight and tries to start at 7am.
Changed the rubber diaphgram, chaneged the pump as it was running very slow, desludged the central heating system in the house, removed the heat exchanger and flushed out. All of this improved the operation and it ran away happily for 2 months. Now the problem is back again. Can anyone tell me if the hydraulic outlet assembly has an internal check valve that may be giving trouble? If i get the boiler going it runs all day and works very well.

Any comments welcome. Thank you in advance for any help.
regards
Malty

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[Puddle]

Well first maybe strip flow switch down again,check still clean,cleaning pin of any black build up and also silicon grease spindle and re assemble,may sound silly but presume you have fitted high head pump,if return filter fitted clean out

 

[Malty]

Thanks Puddle, yeah I did all that , a few times, and it sometimes helped a little in that the spindle comes out barely enough to make the microswitch. If i close down the flow or return valves the pin comes out to its full extent so it,in itself, operates well. The problem in normal operation seems it is trying to overcome a larger pressure or back pressure. Do you know if there is some kind of internal check valve in the hydraulic outlet assembly?