no hot water

robmar0se

Kind if difficult to work out a diagram as there are 7 pipes behind the cylinder (4 x 25mm, 3 x 10mm). The system is vented and have checked the F&E tank (ok). I believe that the pipework around the indirect cylinder is standard as per http://www.diydoctor.org.uk/projects/domestic_hot_water_systems.htm

The arrangement is that the cold water supply comes into the kitchen which is on the same ground floor as the cylinder. All the water feeds to the rest of the house work through the airing cupboard (behind the cylinder). Then on the next floor we have the boiler, pump (working fine) and motorised valves. there is a bath room on that floor too. then on the next floor there is another bathroom, then in the loft we have the cold water and F&E tanks - the system is I understand gavity fed from the tanks, apart from the pump that circulates the heated water.

On the ground floor there are two drain taps, one on a central heating radiator pipe, and another on the "return to boiler" 25mm pipe adjacent to the cylinder. This latter one I was going to try and flush out?

keystone

Sorry - I meant a photograph rather than a diagram.

The usual suspect location for a magnetite blockage is in the pic below in the location where I have drawn a green circle.



There is a BUT though. If there is a blockage there I would also expect the system to be "pumping over" where the hot water goes up the vent and into the F&E tank. If the water in F&E tank is hot or even remotely warm then thats whats happening. However, if the vent is also blocked then it won't. You'll only get partial circulation (or even reverse circulation depending on the severity of the blockage).

Cheers

keystone

Just to add that if the pipe near the cylinder you talk of as being hot is at A and the one at B is cold then you are getting reverse circulation.



Cheers

robmar0se

thank you...............

The F&E water is cold. B is hot and A is tepid/warm.

As a metter of interest, why, in yr experience, does the blockage occur at the vent pipe? And why doesn't it affect the CH systems?

keystone

OK so if pipework around vent feed and valve is hot and its hot going into the heat exchanger in the cylinder at the top but only warmish coming out (I would still expect the coil return to the boiler to be hot to the touch) then everything is clear into the cylinder so we can cross the blockage at the feed pipe possibility off the list.

Its unlikely to be scale on the outside of the coil preventing heat transfer as you've already said you are in a soft water area. Even if it was scale on the outrside then both the inlet and out let pipes should still be hot.

So still thinking blockage bebut now coming round to POV that its an airlock somewhere on the return.

Cheers

robmar0se

As on my system, the lowest point, in terms of gravity, is the cylinder return drain, isn't this the point where sludge etc could build up (all the valves, pumps & boilder are on the floor above)? I also noticed that the boiler return is also warm/tepid to the touch with DHW only on, about the same as the outflow from the cylinder?

As there is a drain plug at the cylinder outlet, it must be worth a shot at draining from here? Living on a hill there is no issue where the water goes, and you never know might just reverse our hosepipe ban!!

PS what would happen if I connected the cold water supply to the drain plug, and forced water in from the mains? Stupid?

robmar0se

Looking at yr diagram, if I drain the system, the expansion tank will force the water out via the line of least resistence, which could be within the cylinder heat exchange, or on the return to the boiler. (i) would it make any difference if the valve was open or closed? (ii) ditto if I connected to the mains and forced water into the drain plug to try to loosen whatever it was (or at least have a go)?

keystone

robmar0se wrote: »

As on my system, the lowest point, in terms of gravity, is the cylinder return drain, isn't this the point where sludge etc could build up (all the valves, pumps & boilder are on the floor above)?

It can build up anywhere but you could be correct.

I also noticed that the boiler return is also warm/tepid to the touch with DHW only on, about the same as the outflow from the cylinder?

I would expect it to be of the same order but warm/tepid ain't right.

As there is a drain plug at the cylinder outlet, it must be worth a shot at draining from here?

It might also be worth a shot of backfilling the system with a hose on that draincock which should drive any air (if there is any) out of the coil. You should also have a draincock on the cold water feed into the cylinder which is also at the bottom. Don't use the wrong one! Oh - you thought of that:

PS what would happen if I connected the cold water supply to the drain plug, and forced water in from the mains? Stupid?

No its not stupid if its an airlock which is what I'm suspecting now from here. It ain't going to do anything for a sludge buildup though.

Living on a hill there is no issue where the water goes, and you never know might just reverse our hosepipe ban!!

Not a chance. Hosepipe ban my fundamental!! :mad: Between them the water companies throw away 3,300,000,000 litres of water each and every DAY through leakage in their supply pipes. Thames Water do nearly a third of that all on their little ownsome. Hypocrisy of the very worst order to impose hosepipe bans.

Cheers

keystone

robmar0se wrote: »

Looking at yr diagram, if I drain the system, the expansion tank will force the water out via the line of least resistence, which could be within the cylinder heat exchange, or on the return to the boiler. (i) would it make any difference if the valve was open or closed? (ii) ditto if I connected to the mains and forced water into the drain plug to try to loosen whatever it was (or at least have a go)?

Posts crossed but the line of least resistance in your installation, which is clearly a little bit unusual as regards pipe runs from your description, is not necesarily directly related to the diagram which is after all a schematic. Theoretically my own system is piped as per the diagram but practically it isn't in terms of vertical runs and horizontal runs and each will be different and each can get airlocks and sludge buildups in different places although looking similar on the face of it. If that pipework is horribly sludged then when you open the draincock you won't get much water initially. I know I'm looking at it (or not looking at it actually) remotely but I still am now leaning towards an airlock in the coil or in the return to the boiler. Is there a bleed valve on the pipework itself at or in the vicinity of point B on the schematic? Have tyou tried opening it and see what comes out?

The valve should be open.

You will have approx 0.5 bar pressure difference between the water tank and the cylinder. Going in the other direction with mains you will probably have approx. 3½ bar but it will also have to overcome gravity. However that 3½ will often shift air that the 0.5 won't. Its exactly the same concept as putting mains pressure cold water the wrong way into a hot tap thats airlocked that you read about here all the time. Make sure the hose is really well secured to the drain !!!! though!!!

Sorry you asked me about the magnetite buildup at the feed pipe connection and I didn't answer. The simple answer (yes there is a more complicated one but its too early for me) is just that it nearly always does and thats the usual place to look for it.

Cheers

robmar0se

Dear Keystone, Thank you very much for yr help, but I believe we now know the problem.

I could not drain nor could I upload direct from the mains, so I believe that the blockage is probably very much at the point of the drain plug. And as you said right at the beginning, we will probably have to cut it out, but at least we have a good idea where it is!