Boiler on the blink, help needed :)

[sinto607276]

The AARV should be at the top of the heat exchanger, it might have a knurled knob that must be loose so that any air in the heat exchanger can vent, The PRV is the safety valve, so if the presure rises to 3 bar it vents to the outside , the other valves are service valves and can be closed so you don't have to drain the whole system, if you close them make sure they are open before pressurising the system (I dont know how or when you do the expansion vessle?) the filling loop is used to fill the system to 1 to2 bar.

Thanks chaz,
I think I've been a bit mixed up with all this.
It's leaking through the pipe outside, takes about 40 mins to build up any pressure (just about 1 bar) to be able to use the boiler, then it loses pressure overnight. So I think it's as I've quoted above, prv replacement job.
Will empty the vessel so no pressure on the prv, take out and replace, pressure up the vessel then hopefully it should work?
Thanks, Colin

[chaz]

It's a while since I worked on gas and not registered now so don't do it any more. On most combi's there are 6 or 7 conections, there's the central heating flow (1) and return (2) pipes these are 22mm, mains cold in (3) 15mm, (the filling loop will go from this to the heating pipe),  DHW (4) 15mm domestic hot water, this goes to the taps, the pipe from the PRV (5) 15mm to the outside, and the gas pipe 22mm reduced to 15mm (depending on pipe run) if its a condensing boiler there will be a (plastic) pipe going outside to a drain.
You shouldn't have to do anything with the expansion vessle as long as its ok, its there so when the water expands on heating it has somewhere to expand into. If the diaphram is damaged then it won't work and when the water expands the only place it can go is out of the PRV, then when it cools there's not enough pressure for the boiler to work?
You should be able to pressurise the system in a few seconds if the system hasn't been drained by opening the valves on the filling loop there may be two one ate each side if the loop,(as its should be removed to prevent contamination but never is).

[sinto607276]

You shouldn't have to do anything with the expansion vessle as long as its ok, its there so when the water expands on heating it has somewhere to expand into.

I put some air in it. It shouldn't be full of air then?

If the diaphram is damaged then it won't work and when the water expands the only place it can go is out of the PRV, then when it cools there's not enough pressure for the boiler to work?
that seems to be what's happening
You should be able to pressurise the system in a few seconds if the system hasn't been drained by opening the valves on the filling loop there may be two one ate each side if the loop,(as its should be removed to prevent contamination but never is).I put the boiler on and it pressured after a while, but don't know if it'll stay up in pressure, looks like I'll be looking at a new diaphram then?
Oh that's way past my diy skillset

[chaz]

this is off youtube.
https://youtu.be/KeO2gswQQe4

[sinto607276]

Ahh well another day.....
After replacing the prv and getting a tad wet I left it last night and woke up to the pressure being at zero.
Thought I'd try and top up the water using the filling loop, heard some water go through and pressure went up a few red lines but not much
So looks like I'm on the blower to a costly repair man to come and sort it