Baxi 105e problems?

I have a baxi 105e with problems. When running hot tap, boiler would deliver then eventually go to lock out. Heating would also do the same.
Have removed main heat exchanger and plate heat exchanger, cleaned with descaler, and also changed pump.
Hot water was then a lot better - Now heating rises to temp then shuts down, then when it attempts to relight as temp drops it fires 2 or 3 times then goes to lockout.
Have adjusted min gas setting as have had that problem before but has made no difference.
Now at wits end!