Noisy gas boiler with near 0 water pressure, how to repressurise?

michaelm

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My old (maybe 25 years) Ideal Classic sealed system gas boiler has become quite noisy. I think it's the water pump trying too hard. Adjusted this through its 3 settings. I notice the water pressure is near, if not, 0. The boiler fires up, the pump kick in, it is heating rads (somewhat) upstairs and down. No air in rads. After maybe 20 mins it gets noisy (or vibrates perhaps) and the analogue pressure gauge might get to 0.3 or 0.5 Bar (so I guess that's working). I switch it off and it goes back to 0. There seems to be air in the the expansion vessel and no sign of leaks generally or water from the external relief pipe.

Anyway I reckon that if I can repressurise the boiler to 1.5 BAR it might start behaving. However, I cannot find a filling loop anywhere. I've found what I reckon is a the heating system's gravity fed water pipe in the hot-press but opening the valve on this does not increase the water pressure on the boiler (is it possible this is air locked or blocked?).

Bit of a Scooby-Doo mystery. Any suggestions before I call a plumber?
 
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Zenith63

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Some photos of your hot press and as many pipes as possible might help somebody direct you to the fill valve.
 

Zenith63

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Any chance of some photos from a little further away so we can see where those pipes are going to/from? Not easy I know :)
 

Leo

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Are either of the two valves in the second picture fully closed?

One of them is likely the feed into the bottom of the hot water cylinder. If both are open, close them one at a time and see which stops the flow from a nearby hot tap.

If the other doesn't seem to affect flow to any other taps, and you can't see where it is going to/from, it may be the filling loop. Close it when the heating system is cold. Then run the heating for a while and see does the pressure rise as the water heats up.
 

Zenith63

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Are either of the two valves in the second picture fully closed?

One of them is likely the feed into the bottom of the hot water cylinder. If both are open, close them one at a time and see which stops the flow from a nearby hot tap.

If the other doesn't seem to affect flow to any other taps, and you can't see where it is going to/from, it may be the filling loop. Close it when the heating system is cold. Then run the heating for a while and see does the pressure rise as the water heats up.
The tap on the left looks like it has a non-return valve right at the top of the photo, so I'd say you're most likely correct, would just like to see where it's going to/from to be sure.
 

michaelm

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@Leo a different pipe runs to the bottom of the hot water cylinder, it is not in the photo. @Zenith63 the tap on the left is closed and I'm pretty sure that is a non-return valve (photo attached). Unfortunately, when I open it, the pressure on the boiler is unchanged.

View attachment DSC_0275c.JPG
 

Zenith63

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Yep definitely a non-return, the only place I have one in my system is on the fill-valve. On my system, the pressure can take quite a while to actually start to go up, have you tried leaving the tap wide open for a minute or two? In theory the fill circuit is not supposed to be left connected at all times, you'll often find a piece of flexy hose that is supposed to be disconnected each time you fill the system. Any chance that circuit is disconnected in this way further up (possibly in the attic or next floor up) or that there's another valve further up?
 

michaelm

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Yeah maybe there's another valve in the attic somewhere. I'll crawl around at the weekend. Thanks for all replies.
 
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