Air lock in plumbing system

[myles]

I have a towel rail in the bathroom which gets its hot water from the hot water cylinder , the return being directly back to the cylinder . It is NOT part of the central heating system. As a result of some fiddling with the supply of cold water to the cylinder simultaneously with the running of hot water taps the rail now fails to heat , absolutely stone cold. I have of course tried to bleed the rail but this has no effect although if I let water dribble out of the bleeding point for long enough warm water appears and the rail partly heats up but clearly the water is not flowing through the rest of the rail back to the to the cylinder.
Although no expert ,I feel reasonably sure that there is an air lock probably not in the rail (otherwise bleeding would free it up) but in the return pipe from the rail back to the cylinder. Unfortunately I cannot detect any drain cock which would allow me to drain the cylinder and hopefully get rid of the air. Also the system is pretty old so I am very reluctant to get into pipe work.
Here is a rough diagram of layout of the towel rail:
B __________ A
l l
l l
l_ ________ l __V___ D

A=Hot water from cylinder; this is a spur from the pipe which takes hot water from the cylinder to the hot water taps. B= Bleeding point ; V=on/off valve ; D=return pipe which connects to cold water supply pipe to cylinder. The pipes connecting the rail to the cylinder are about 4 feet long and the top and bottom of the rail are at approx same levels as the cylinder.
I am wondering whether given the way the air lock got there in the first place it may be possible by some combination of shutting off/on the cold supply to the cylinder and operating the bleeding point on the towel rail and opening/closing hot water taps it may be possible to get the towel rail back into use.
I would be very grateful to hear from anyone who can offer solution or suggestions for me to try. Thanks!

 

[masona]

Is this a new projects ? or has the plumbling system been interfered.Try looking at this website for better understanding www.towelrails.co.uk/aquastar.htm

 

[MANDATE]

A hot water cylinder has the cold water inlet near the bottom and hot water is drawn off from the top of the cylinder. When a hot water tap is opened the water is forced out under a slight pressure, which is dictated by the distance between level of water in cold water cistern above(tank) and the top of the cylinder.
The idea of draining the cylinder to me seems pointless,that is allowing more air in.I would say with the water outlet at the top you cannot have a airlock in the cylinder,any air in this area would go up the expansions/overflow pipe which is taken off the pipe going to the taps as it leaves the cylinder.
I would be looking at the pipes going to and from the rail to see they are slightly angled and if air could accumalate in place where it can/t be bled off.
If it's not part of the central heating I imagine there is no pump to circulate the water through the rail and relies on convection only, this lack of pressure means the slightest of resistance will affect
I would be looking at the valve maybe not fully open
Although its not part of the central heating I would bleed the rail when central heating circulating pump is operating, some of the pump pressure could help.
I would also consider turning the valve off between cistern and cylinder and opening the uppermost hot water tap, I would attach a short piece of hose and blowing down this may dislodge any air.don't forget to open the valve again

 

[myles]

Is this a new projects ? or has the plumbling system been interfered.Try looking at this website for better understanding www.towelrails.co.uk/aquastar.htm[/QUOTE]

Thanks for this . I am trying to fix an existing sytem.

 

[myles]

Mandate

Many thanks for your prompt and helpful reply.

I'm pretty sure you are correct in identifying where the trouble is .Given that bleeding does ultimately result in warm water from the bleeding point I think this points to the trouble being in the short pipe from the towel rail on/off vale to the hot water cylinder.

I took your advice and had a look but unfortunately access is a big problem (floor boards !) but in the two or three feet of pipe I can see there must be a couple of 90 degree bends ; so this could well be where the problem is.

I turned off the valve you mentioned (on the cold water supply pipe to the hot water cylinder) and ran the highest hot tap. This gave about a litre of hot water after which I attached the hose and started blowing but got no result , although after each blow a small trickle of water came back out of the tap.

I also checked the on/off valve on the towel rail to check it was on OK. I suppose it is possible that although its handle turns there may be a failure to open it . I can't see a way to check that .

Meanwhile my thanks again and I shall persevere with the blowing.

 

[MANDATE]

Right let me see, how about closing the cold water feed valve again and instead of blowing you could do with forcing some water back from the hot tap. How about a longer piece of clear plastic tube fitted to the hot tap held vertically(except the bottom bit) with a funnel at the top(the higher the better,) then pour some water into the tube and the pressure should push the air back so it can escape up the vent pipe,once gone it can't get back,
Then close hot tap before removing tubing.
It's worth a try, I've used this method to move an airlock in an oil fuel pipe line.
The problem is that air is compressible and you need a bit of pressure to move it either forward or back until it can rise and escape or be bled off
I think I've just invented a big syringe 4in diameter 30in long holds about 10litres of water bit of tube, so close valve! fit syringe!open hot tap!push in water! airlock gone! close tap! open valve! submit bill

 

[myles]

I've been away and am only now getting to grips with your most recent suggestions.
Unfortunately the taps are so designed to make it difficult to connect a hose in a nice tight way but
the connection I have managed is pretty good. So far trying to push water through does not seem to have produced any movement . To me it seems that the pressure I am applying is being split three ways ; to push water back into the hot water cylinder or up the overflow vent or through the hot water supply pipe to the towel rail and thence to the return pipe from the rail to the cold water inlet to the cylinder.

If this is the right way to think about it then it looks as if LOT of pressure may be required .

I'll try and get some better fitting hose this weekend and see if that helps.

Again my thanks to you.

 

[MANDATE]

Apart from blockage,ie sludge in a radiator or stuck valve I think there two types of air pocket problems.
Air in a radiator (or towel rail in your case) preventing the radiator getting hot, which is cured by bleeding the air off the top of the radiator.
The second type is where there is a air pocket in the pipework, perhaps where a pipe goes up then along then down, and preventing a radiator from receiving hot water.This is like a inverted 'U' tube and when a system is being refilled water goes up both sides and traps the air
In this case I feel bleeding the radiator has no effect because, probably there is no air to bleed off, only water, and the flow of water is so small that water can enter and leave the air pocket without moving the air pocket along to either a radiator (where it can be bled off) or the overflow vent where it will escape without bleeding.
This type of problem can sometimes be cured by increasing the pump speed or removing the radiator (after closing the valves) and fitting a length of tube and running of a couple of bucketful of water at a faster rate and the air pocket.
I have fitted clear plastic tube to both valves and with the system on you can see if water is passing through and if it contains air.
Lets hope you have some success