it sounds like you are paying privately for the repair & you dont trust your plumber/gas engineer
you can always ring the boiler manufacturer & explain the situation
if you were watching the plumber working and can remember what he did, the manufacturer would ask if certain items were checked/tested before the plumber decided on which part needed replacing
other than that your only choices are to go with this plumbers diagnosis or get an independent opinion/diagnosis from another gas engineer
if you decide to go ahead with repair i would strongly recommend you keep hold of old defective part
you can then get it tested independently to check if it is faulty
Q, May 2014
