unable to repressurise Worcester 28CDi after drain down

garyo · 27 Sep 2006

Hi,

I've just drained all my first floor rads to change some pipe work. The boiler is also on the first floor.

After inserting the filling key, and opening the grey valve, nothing happens. There's pressure getting through to the grey valve, as I can remove the black screw cap on the other side of the key and there's loads of water pressure. I'm dong this with all the rads in the house on, with bleed valves removed, and theres not even a hiss from one of them.

I've gone though the documentation, and the system was fully working before I did this - so am I missing something obvious?

One thing I'm wondering is what's in the black plastic housing just on the other side of the bleed key - some kind of non-return valve I guess - does thiis ever get stuck? Oh, and I've bled some pressure from the main pressure vessel thinking this might help make the external water pressure overcome some internal valve, but no joy.

Cheers

Gary

Gasguru · 27 Sep 2006

With the gauge on zero check the pressure in the red expansion vessel.

This should be about 0.8 Bar. Do not attempt to refill without checking this.

When you open the grey valve can you hear the water flowing? What does the pressure gauge show. You will need to have the valve open for some time to refill and pressurise all the radiators.

On the other side of the key is a check valve arrangement - I have not heard of these sticking.

Rob · 27 Sep 2006

double check that BOTH ends of the radiators are open . i beleive because of the diverter valve it will only fill via the return.

ollski · 27 Sep 2006

Did you drain it through the pressure relief valve?, shut the isolation valves etc?

garyo · 27 Sep 2006

Thanks for the replys.

I closed the valve so that the mains were cut off, but without the filling loop key in I guess that has no effect anyway.

I didn't shut the isolation valve on the back of the boiler that isolate it from the heating pipework

I drained it by connecting a hose pipe to the drain valve on a ground floor rad, and then drained enough so that the work I was doing upstairs didn't have water in it.

I've just tried to check the pressure in the expansion vessel, but don't have a schraeder valve flexible extension, and the access it too awkward to get my gauge in without. I'll report tomorrow.

When I open the grey valve I can't hear a thing. The system pressure gauge is still on zero, regardless of whether I have the rad bleeds open or closed, or grey valve open or closed. I have both bottom valves on all rads open... When you say 'some time' do you mean hours or days?

Cheers.

Gary

pannierstan · 27 Sep 2006

I bet the plastic inside the grey knob is stripped and you are actually not turning the valve its self. Try removing the knob and check the condition of the shaft.

Stan

garyo · 27 Sep 2006

Hi Stan,

Yep the white plastic shaft is coming out. If I unscrew the cap off the black checkvalve, then I can make water flow out of the cap by opening/closing the grey valve, so the water is getting across the filling key, but then no futher.

Gary

pannierstan · 27 Sep 2006

Hmmm, does indeed sound like a problem with the back check valve but as mentioned by others I havent had this issue.

Have you got plenty of mains pressure at the cold taps and is the main stop tap fully open?

garyo · 28 Sep 2006

The pressure feels good to me. With the cap off the black valve housing I can just about keep my finger over the top of the opening with the grey valve open. If I lift off slightly I get the expected two foot of spray!

Mmm I was hoping someone would say I didn't drain down correctly, so there's an airlock in X which I fix by doing Y

ChrisR · 28 Sep 2006

Don't know exactly where the check valve is - anyone??
These bits come apart fairly easily. There's a bit of bent metal designed to do something or other which just gets in the way but I'm sure you'll manage! Those metal tabs slide out...
Pic if it helps

The next place the water should pee out from is the drain screw on the flow manifold behind - got it?

garyo · 28 Sep 2006

Thanks for the picture Chris... that's exactly the bit I'm struggling with. As far as I can tell the check valve in in the top left of that part in your picturem just above the 'passed inspection' picture. It's a diaphram shaped housing.

I've not checked the drain screw - I'll do that next and see if there's water in there, and maybe I'll slide those metal tabs off and take a look in there too.

Cheers

Gary

Rob · 28 Sep 2006

try turning the boiler on and off at the mains whilst filling loop open

garyo · 28 Sep 2006

I've made some progress. After removing the black plastic assembly and giving the valves a good clear out, I noticed that the hole in the boiler leading to the rest of the system was blocked off. It was a 1mm thich wall of fairly solid black... er... grit/grime.

I removed this with a jewelers screwdriver and then water started to flow backwards from the rest of the system. I slid a compressed 'air duster' nozzle about an inch into the hole and gave it a good clear out, and now everything is working fine again.

Is the layer of black stuff on the inside bad news.... a sign that there's been no anti-corrosion agent in the system?

Thanks for all your help - all that was needed was the confidence to delve a little deeper!

Gary

ChrisR · 29 Sep 2006

That surely must be clag from the mains, there wouldn't be any flow to/from the heating system? The small hole would be to restrict the rate at which you can fill the boiler, as it can (we are told) do damage if too fast.
I've been sketching again.

garyo · 29 Sep 2006

the wall of 'clag' was at point 104 in the diagram - pretty much sealing the hole in the o-ring. After I removed housing 109 all I saw was the black wall.

I'm not sure if there'd be flow past that point looking at the diagram it seems there might be, but I'm not familiar with the workings...

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unable to repressurise Worcester 28CDi after drain down

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