Right....so.......when tap on thermostat opened and flame lit, gas opens full rate thru thermostat valve & into FSD/burner, when thermostat reaches required temp valve closes......but still maintains temp thru by-pass to burner, when stat cools down valve opens again (depending on setting) increasing gas to burner therefore increasing temp & so on.....if flame was to go out FSD would close valve to burner?
Um. Keep it simple and precise. Look at the drawing and I expect the steps make more sense. Don't confuse the function of each part:
eg
when tap on thermostat opened and flame lit, is confusing the lighting, with the thermostat. It'll light at any thermostat setting
but still maintains temp thru by-pass to burneris confusing the temperature control with the bypass. The bypass is there only to keep the burner alight. The thermostat valve is there to regulate temperature.
You'll obviously get through fine with the knowledge you have, but it'll be easier if it's all clear in your mind.
There are lots of "surprising " candidates, like the guy who was on his 3rd 5year retake and didn't know let-by pressure.
I keep being told there's a liquid in a thermocouple
Many have no idea what a draught diverter is
Most don't know how to check that a FFD, on say a grey button gas valve, isn't letting by
Everyone condemns a wooden chimney which has a liner in it
Many think existing pipework has an acceptable leak rate
Most don't know why positive pressure boilers are dangerous
Apparently you can check for let-by by smothering the handle with ldf
A major problem is that candidates can turn up claiming experience when they don't have any. They have to get a signature of a corgi to say they have, but there's no shortage of liars, and no follow-up.
Still plenty of stuff I don't know, or find I've been getting wrong, by the way!
If a cable's in a plastic conduit but within 25mm of gas, is it OK? Regs say Insulating Panel makes it ok - plastic is insulating. I don't know!
Fitz as far as I've seen some of the questions are as daft as ever. There's a rumour that some of them are deliberately misleadng so CITB etc can be suspicious if everyone gets them right!