Hi Grll,
I really am on a learning curve, the best thing to date I think is the variable resister that makes it so easy to test if the thermister is at fault. I have made one up with a simple start type button that you have to hold down all the time you are testing I included this in case I forget to take the connections off and blow the boiler up. If you want some more detail of the one I made I will send you a photo and details.Another good tip I got was to use the test point at the top of the boiler, connect your U gauge and see if youare getting the right vacuum, I am still trying to get my head around this one. I have got a stack of invoices to do so I will talk 2 U later.
Regards
Jim
PS Have you found any good ones yet?