15 Apr 2010
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United Kingdom

Wondering if anyone can help wi this?

Drained system via combi boiler valve. Opened bleed valves upstairs(1 in attic conversion and 4 on 2nd floor) no water coming out. Left for a good wee while, closed and went downstairs. 4 rads on ground floor still had water coming out when opened bleed valves???????

Ended up removing rad on ground floor(which was whole point of operation) due to cold spot. Left trv and lockshield valves open. I drained a further two and a half buckets(over 20 litres) out of system via old chinese container.

Flushed out rad with cold spot and re-filled system.

Anyone got any idea why system not draining fully via boiler(drain point is lower than ground floor pipework)? I was intending putting some fernox cleaner in next then inhibitor. Might not bother as instructions with cleaner say to refill and drain a few times to make sure all cleaner out of system then stick in inhibitor. Might just put inhibitor straight in now.

Might be worth a cuppa and bacon roll for best answer if local.

Any advice greatly appreciated,

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The rads on the ground floor aren't piped from drops from the ceiling?

Opening the bleed valves on the downstairs rads can help drain them (obviously only open downstairs bleed valves after everything above has drained) - not opening the valves can create a vacuum that prevents the rad draining. Sometimes a wet vac can help speed things along.

Whilst you have the system drained down, consider fitting drain off valves on the problem rads.

Too far to go for that butty. Can you post it? ;)

Thanks for reply.

Butty in envelope, what's the address?

Ground floor rads are piped under ground floor.

Any idea why the system not draining fully from boiler?

Just to confirm, you drained via a drain cock that is below floor level, as you mention via/from boiler?

You also opened the bleed valves on downstairs rads?
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Yes that's correct.

Not so much draincock, more of copper pipe that runs vertically down from combi to underfloor.

It is lower that heating pipework on groundfloor though.
Is the boiler lower than the ground floor radiators, or just the pipe outlet. Is there a valve on the drain pipe? If so is it at boiler level or at the pipe outlet?
Or... perhaps you opened the Pressure Relief Valve?
The important point is the level where this pipe joins the system near or at the boiler, not the level of where it ends. If the draw off is at the boiler which is level or above the level of the rads and pipes, then this will prevent draining.

As Denso says, if it's the PRV, then it's not a good idea to disturb these.

A pic may help.
Might be getting somewhere here.

Boiler is on ground floor but is higher than ground floor rads.

Outlet pipe is lower than ground floor rads pipework. It runs vertically down from combi under floor.

There is no valve as such on pipe outlet. The valve I have operated is inside the boiler beside pressure guage.
You will be draining the boiler and everything above it but not the ground floor rads. As Whitespirit says, not a good idea to use the PRV in the boiler. You should have a drain cock somewhere else for the heating. Nothing which looks like the pic Whitesprit put up earlier sticking out of the building at a low level?
I can post pic tomorrow, but from what you guys are saying I've been messing about with PRV at boiler.

I am 99.9% sure I do not have draincock/valve anywhere on my system. There is definitely nothing on any ground floor rads or sticking out from house.

Might be under floor, but I can't remember seeing anything like a draincoock on any pipes under floor.

Might have a double check on pipes under floor.

Is this normal to not have a draincock somewhere?

Big job to get one fitted?

PRV nothing to do with draining system?

I'm a numpty?

The 2 detectives cracked the case - possibly.

If you haven't got one of these -

either under the boiler or on the downstairs pipework, fit one of these

in place of one of your downstairs rad valves.

And stop playing with it. The PRV that is!
Is this normal to not have a draincock somewhere?

Should be one somewhere. Some systems have a wheel-head gate valve fitted below a floorboard, with a pipe leading to the outside to drain. Unusual to have no drain off at all.

Easy job to fit one of those drain off rad valves.
That's 2 cuppas and 2 bacon rolls then?

What is PRV then, purely for boiler?

Don't suppose you have a picture of wheel-head gate valve in your extensive album do you?
It's a pressure relief valve in case there was a problem with boiler, and pressure exceeds safe limit. It will open to vent hot water out of the PRV pipe safely to the outside.

Sometimes, if you drain water out of them, bits of crud from internal corrosion (mainly ferrous from rads) can get lodged in the PRV and cause it to leak leading to pressure loss in system.

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