Potterton Lynx 1 Flow rate problem..?

[Robinm]

Thanks for all the previous posters who helped me narrow down what the problem was.. there's more to these things than meets the eye! Blimey.. I thought completely 'electrical and electronic' before but read this and see what you think..?

Here's the symptoms: Turn DHW bath tap on full.. lots of flow, boiler ignites, high flame etc. all works normally, temp doesn't get very hot (about 40 degrees), switch to shower with lower flow and the boiler turns the heat off..

Also if a DHW tap is on and then a cold tap is opened (even just a half a turn) the heat gets turned off then as well. Must be a flow switch or diverter valve problem? any idea's gratefully received, I did go down the electronics route first (but board is good, as is the DHW temp sensor, (Ohm's all normal)..

Sorry to be a pain! I'm determined to fix the blinkin' thing.

Thanks again.

 

[gas4you]

Could be a dirty or blocked inlet filter causing a flow rate less than that required to keep boiler working

 

[nickso]

id start with the diaphragm. its maybe stretched and only hitting flow switch at higher flow rate. the inlet filter is in the same housing so can be checked at the same time anyway.