Potterton Combi Question

[john2k]

Today I had Baxi come and replace a filling loop which was leaking on my Potterton Combi boiler. I wasn't home but my wife tested the radiator afterwards and she said it got warm. But when I came home I noticed that while changing out the loop, the engineer must have shut the main valve at the return just before it enters the boiler, as the filling loop is connected to that it allows him to disconnect the loop. He also shut the valve that is the central heating output. So basically He left it with the central heating out and return both turned off. So when I came home and turned heating up the boiler was making a strange noise and heating wasn't coming on. I discovered these valves were shut so opened them and now seems to be ok. Question is with these valves off and if the boiler ran trying to provide heating was any damage done?

 

[Newboy]

Unlikely - the boiler has overheat protection

 

[john2k]

So with both valves shut the pressure and heat was technically just building up inside the boiler? how does it release the pressure if it's too much? pressure relief valve? Also, with the boiler cold and rested, i filled the pressure to the pressure shown in the pic below, but when I turn heating on the pressure goes just before the end of the green zone. If I watch it carefully it starts to drop again and raise again. Is this normal? Is there a safety mechanism to prevent it from going to the red

 

[Newboy]

So with both valves shut the pressure and heat was technically just building up inside the boiler?

Yes

how does it release the pressure if it's too much? pressure relief valve?

Yes.

but when I turn heating on the pressure goes just before the end of the green zone

That's OK

If I watch it carefully it starts to drop again and raise again. Is this normal?

As the boiler heats up, the pressure will rise and as it cools the pressure falls again - there is an expansion vessel to allow for the increased pressure.

Is there a safety mechanism to prevent it from going to the red

There is a pressure relief valve to deal with excess pressure - you will find a PRV discharge somewhere close to the boiler (hopefully with nothing discharging from it!).

If there is a discharge (or signs of a discharge) from the PRV then it's worth getting the PRV and expansion vessel checked.