CH Wont Drain

[Rally Matt]

HI, I might b going over old ground here, sorry if I am! I am fitting a towel rad in bathroom. needed to drain system as it needed alterations to pipework. I have a vented pumped system y layout. I disabled float valve in loft, opened bleed valves, and opened up drain valves in ground floor rads. I only got a very small amount of water out. The rad in bathroom has been removed, ok. I noticed the header tank didn't loose any water thru draining. The system now wont run properly, boiler keeps going out after a few secs and some loud bangs, so I guess there isnt enough water after trying to refill system. Pump seems to run but gets very very hot. We live in a bad area for limescale and there is quite a build up of crud on outside of pump fittings, no leaks now tho. watever i do cant seem to get system to drain though and therefore bleed properly. I did find the bypass valve had been closed off in airing cupboard, is this a sign pump/motor valve isnt working and needs replacing? I am quite happy changing components and pipework etc if someone has educated guesses to my problems.

 

[oilman]

Don't change any parts until you've sorted the problem of the tank not emptying. There is a blockage in the cold water feed, ie the outlet from the tank, and it is near where the feed pipe meets the first hot circulation pipe. There is no alternative to cutting the pipe and mechanically clearing the blockage. Chemicals will not work.

Put a bung in the tank outlet before you start or you will be deluged by 15 or so litres of cruddy water.

 

[Rally Matt]

The water in the small header tank is clean. My next idea was to remove the pump and see if water started to flow from header as a result (into a bucket with ball cock disabled again). I based this idea on the fact there was a pipe leading from small header to pipe which feeds both pump (lower) and I guess the boiler input. The house is only 9 years old so could it be badly affected with gunge in system already?

 

[oilman]

It's not gunge that is a problem but a build up of lime scale and corrosion products in the pipework at one particular place. Your idea of removing the pump first to have a look is a good one, it might reveal something. I am surprised the header tank water is clean though, I would expect it to be rusty around the tank sides and on the bottom.

 

[Rally Matt]

The header is plastic and all the pipes are copper so I guess rust marks would b unlikey. Im planning on the pump removal, if only to check for blockages further up the system,tomorrow morning. I hope I haven't missed some really obvious bleed/drain valve somewhere but i am bug**ed if I can find any more! The motorised valve is a Drayton Flowshare 2, and seems to have 2 posistions, 1 for htg and 1 for hw, but can hover between the 2 for a combined setting. Is that a 2 or 3 port version should I need to change it? The pump is a Grundfos super selectric. It makes a noise when the control panel is activated but is it normal for buildup of lime crud around the joints? If it like that on the outside what is the inside likely to be? I'll let you know how I get on with the next thrilling installment!

 

[oilman]

The valve is a 3 port mid-position.

Scale around pump joints is common but a bad condition. It doesn't mean you will have scaling inside the joints though. Replace the pump joints, they're not expensive. Make sure you use the gate valve type though.

The rusty coloured substance is generated in the radiators and gets to the tank via the vent pipe over a long period. I often clean the tanks out. even plastic ones.

You should hardly hear the pump running.

 

[Rally Matt]

Ok after a frought day we seem to have made some progress! In the end I couldn't get any water from the header to the rest of the system, I cut the pipe feeding the system in the airing cupboard and syphoned out the header. I found a drain screw in the boiler and remocved that, a small amount came out. Finally I removed the pump and motor valve. The pipes all seemed clear so we then primed the system via a hosepipe and funnel very slowly letting the system refil. The pump was refitted and a new motor valve. Things seem to be working to an extent however the lower rads dont want to heat up unless the tops are switched off and then the lower sections of the rads are cold. I have tried balancing the rads but without a thermometer its prob not right yet. Any further tips welcome!

 

[Gees]

Did you reconnect the header tank?
If you didnt the sytem will have no Head of water to force the air out of the system... When you cut the pipe did the header tank empty through the cut end?

 

[Rally Matt]

Yes, after priming the system manually I refitted the header and released the ball cock, all that part of the system seems fine, I think it was the air lock from hell that was preventing the fall of the header water to refill the system. Just a daft question, the gate valves on the ends of the pump, which way should the little oval spindles point, I presume it is line with flow? ie vertical for open or are they screws? clockwise for fully open?

 

[Gees]

If the valves are closed nothing would work and the boiler would "kettle" the valves are a 90 degree type normally with the slot parallell with the pipe when they are open. If you still have an airlock you could try reversing the pump and see if that would help. dont forget to put it back though.
When you bleed the rads does the water realy spurt out under pressure on each one? if it just trickles out then you may still have a blockage

 

[Rally Matt]

Thanks for that, I guessed it would b but sometimes u find things in life that are not logical! The airlock has been cured, by manually refiling system down the pump inut pipe (with pump removed) the whole system now is pretty air free, i'll keep bleeding all the rads over the next few days just to fin tune it! I got heat thru the lower rads by draining them until hot water came out, water ran very clean so i think there is not a serious sludge prob there, just need to balance all the rads to even out the heat flow.