No Hot Water - Gravity Fed System

[Monkey Wrench]

The system : S plan with the hot water cylinder in the loft and the F&E tank about two feet (max) above the cylinder. The cold feed from the F&E tank and the cylinder flow/return disappear into the eaves of the roof (inaccessible), run down some boxwork in the first floor hall and then re-appear under the hall floor together with the two diverter valves and the circulation pump. The boiler is a Rayburn located in the kitchen.

I replaced the hot water zone valve (head and body) on a gravity fed system last week but, despite all attempts, I've been unable to get the hot water circuit working again. I part drained the system (first floor only), replaced the valve body, then refilled the system without a problem. I went up into the loft to check that there was water at the cylinder flow & return, but unfortunately not ! I therefore loosened the Auto air vent connected to the flow to the cylinder, got quite a bit of air and then finally, after running the heating/hot water for a few minutes I had water at the air vent. However, when I loosened the nut at the flow connection on the cylinder boss/flange there was no water ???? Weird ! I assumed the system just needed a little "run" time to dispel any air locks and so installed a new auto air vent at the cylinder just in case the old one was stuck/jammed. The heating was working fine and the boiler wasn't locking out.

I told the customer to run the heating/hot water for a few hours/days and this should resolve the problem. The customer (very relaxed and laid back) said fine and today (a week later and after me thinking all must be ok), texted me to say they still had no hot water ???

For reference, I installed a new bathroom radiator on the same system about six months ago and again had to partially drain the system but had no problem restoring the hot water circuit.

I'm going back next week to have another go but I'm running out of idea's as to how to get the hot water circuit back again. There are a couple of air vents under the hall floor and but have water, the pump has water, the heating works, theres water at the cylinder air vent but (last time I looked) not at the cylinder ???

Any help/suggestions would be much appreciated, thank you.

 

[SimonG]

Pull stats and boil it.

 

[Roger Welton]

Pull stats and boil it.

May need new underwear if its your first time doing this :toilet:

 

[SimonG]

Ferrous gonads

 

[Monkey Wrench]

Pull stats and boil it.

Thanks for the post SimonG.

I've got to say that I'm not familiar with the solution you're suggesting and so some more info would be appreciated.

I take it that you mean bypassing the immersion stat and then leaving the immersion on !?

Is that a way of drawing air out of the flow/return pipes ?

Thanks again.

 

[Best]

Maybe magnetite in the flow or return pipes to the cylinder and when you drained system pipe that was nearly blocked, sealed up completely. Check with a magnet at any tee, - especially on return at coil & pipe below it.

 

[Best]

Thanks for the post SimonG.

I've got to say that I'm not familiar with the solution you're suggesting and so some more info would be appreciated.

I take it that you mean bypassing the immersion stat and then leaving the immersion on !?

Is that a way of drawing air out of the flow/return pipes ?

Thanks again.

I think he means even more scary - using the boiler!

 

[Best]

Just thinking, - can you not very carefully link mains to flow & return at cylinder, one at a time and check if water passes through from one to the other?

 

[Monkey Wrench]

Maybe magnetite in the flow or return pipes to the cylinder and when you drained system pipe that was nearly blocked, sealed up completely. Check with a magnet at any tee, - especially on return at coil & pipe below it.

Thanks for that Best, certainly worth a look.

 

[Monkey Wrench]

Just thinking, - can you not very carefully link mains to flow & return at cylinder, one at a time and check if water passes through from one to the other?

I could certainly try that so again, thank you, I'll give it a try.

 

[Monkey Wrench]

I think he means even more scary - using the boiler!

Hmm, I think I'd need a pair of the The Wrong Trousers to try that one ;-)

 

[Monkey Wrench]

If I find that the cylinder flow/return pipes are blocked with magnetite, whats the best way of breaking it down and clearing it ?

Thank you.

 

[Monkey Wrench]

Pull stats and boil it.

I'm certainly not brave enough to try this, particularly as it seems you mean bypassing all stats (boiler included). However, I'm curious to know that, as there's no flow/return from the boiler to the cylinder (and hence no water), how boiling would cure the issue ?

Thank you.

 

[joni os]

Go with Best. Get your magnet out. Cut out and replace effected area.

 

[Monkey Wrench]

Thanks for that Joni so.

I just hope the blockage isn't in the cylinder coil itself !

 

[Monkey Wrench]

Ok, so I went back last Monday and, before checking pipework with a magnet, turned the hot water and heating on. As previously stated, the hot water cylinder is in the loft and the flow/return pipe run from the Rayburn in the kitchen to the cylinder in the loft (via pump & diverter valves under first floor hall) is about 30-35 feet. After turning the hot water/heating on, I went straight up to the loft to check the cylinder (took a couple of minutes at most) and the flow pipe to the cylinder was already getting warm and after another minute was hot. However, after a few further minutes, the return pipe hadn't warmed up at all.

I then part drained the system, disconnected the flow/return from the cylinder and ran some water through the cylinder (not mains pressure but using a bottle of water) and, apart from a bit of discoloured water coming out the other end, found the cylinder coil to be clear.

I've checked 50% of the flow/return pipework to the cylinder with a magnet (the other 50% is in a difficult to access loft/ceiling void) and it's clear.

Surely, if there was a blockage, there's no way the flow pipe at the cylnder would have warmed up so quickly (if at all) as there's no where for the water to go !

 

[Best]

Ok, so I went back last Monday and, before checking pipework with a magnet, turned the hot water and heating on. As previously stated, the hot water cylinder is in the loft and the flow/return pipe run from the Rayburn in the kitchen to the cylinder in the loft (via pump & diverter valves under first floor hall) is about 30-35 feet. After turning the hot water/heating on, I went straight up to the loft to check the cylinder (took a couple of minutes at most) and the flow pipe to the cylinder was already getting warm and after another minute was hot. However, after a few further minutes, the return pipe hadn't warmed up at all.

I then part drained the system, disconnected the flow/return from the cylinder and ran some water through the cylinder (not mains pressure but using a bottle of water) and, apart from a bit of discoloured water coming out the other end, found the cylinder coil to be clear.

I've checked 50% of the flow/return pipework to the cylinder with a magnet (the other 50% is in a difficult to access loft/ceiling void) and it's clear.

Surely, if there was a blockage, there's no way the flow pipe at the cylnder would have warmed up so quickly (if at all) as there's no where for the water to go !

Yes, the flow pipe can heat up fairly quickly as it is only the water in the pipe heating up. It may only be passing through it very little due to a blockage or air lock. I see this very often on a cylinder with return pipe nearly blocked totally. Something strong, but flexible pushed down into pipe would be handy.

 

[SimonG]

Airlock.

 

[kris]

Ok, so I went back last Monday and, before checking pipework with a magnet, turned the hot water and heating on. As previously stated, the hot water cylinder is in the loft and the flow/return pipe run from the Rayburn in the kitchen to the cylinder in the loft (via pump & diverter valves under first floor hall) is about 30-35 feet. After turning the hot water/heating on, I went straight up to the loft to check the cylinder (took a couple of minutes at most) and the flow pipe to the cylinder was already getting warm and after another minute was hot. However, after a few further minutes, the return pipe hadn't warmed up at all.

I then part drained the system, disconnected the flow/return from the cylinder and ran some water through the cylinder (not mains pressure but using a bottle of water) and, apart from a bit of discoloured water coming out the other end, found the cylinder coil to be clear.

I've checked 50% of the flow/return pipework to the cylinder with a magnet (the other 50% is in a difficult to access loft/ceiling void) and it's clear.

Surely, if there was a blockage, there's no way the flow pipe at the cylnder would have warmed up so quickly (if at all) as there's no where for the water to go !

When u emptied the system did u manually open the zone valves to allow proper filling of the system , ?

 

[Monkey Wrench]

Thanks again for the responses.

Yes, the flow pipe can heat up fairly quickly as it is only the water in the pipe heating up. It may only be passing through it very little due to a blockage or air lock. I see this very often on a cylinder with return pipe nearly blocked totally. Something strong, but flexible pushed down into pipe would be handy.

Ok thank you, certainly worth a try with a sturdy piece of flexible hose pipe.

Airlock.

Thank you, but I've loosened both the flow and return connections at the cylinder and there's water at both. There's also an auto air vent on the cylinder flow pipe so surely any airlock would have vented out through that by now !

When u emptied the system did u manually open the zone valves to allow proper filling of the system , ?

Thank you, yes, I manually opened both zone valves.

 

[Best]

You can still have an airlock. Pipes will fill up with water but still leave air trapped somewhere on a level pipe or high spot. Might be best to try a careful blast of mains water through them if all else fails.

 

[Monkey Wrench]

You can still have an airlock. Pipes will fill up with water but still leave air trapped somewhere on a level pipe or high spot. Might be best to try a careful blast of mains water through them if all else fails.

Thank you, yes, definitely worth a try before I start trying to push something down the pipe. Where do you think the best place to connect the mains feed would be, in the loft near the cylinder ? If so, I'll have to do a partial drain in order to fit a tee and and an isolationg valve.

I guess I'd obviously have to open the drain valve at the same time as blasting the mains water through otherwise the F&E tanks going to fill up rather quickly !

Thanks again.

 

[lucas121]

We recently worked on a plastic sealed system that must have been poorly installed as there were air locks everywhere, even when it was fed by mains pressure.

In the end we had to connect the power flushing machine, cleared the air locks in seconds.

 

[Monkey Wrench]

We recently worked on a plastic sealed system that must have been poorly installed as there were air locks everywhere, even when it was fed by mains pressure.

In the end we had to connect the power flushing machine, cleared the air locks in seconds.

Thanks for that but unfortunately I don't have access to a power flushing machine. I guess I could always try and use a powerful wetvac but I haven't a clue how I'd connect the nozzle to the drain off !

 

[Coldfeed]

It was hard for me to get what your saying. So are you saying you changed the motorised valve for the hot water/ so the coil one yet your not getting hot water out the cylinder but you've got hot water to the valve

 

[jam1979]

Has the cylinder got water in it by that I mean have you checked the ball valve for sticking

 

[Monkey Wrench]

It was hard for me to get what your saying. So are you saying you changed the motorised valve for the hot water/ so the coil one yet your not getting hot water out the cylinder but you've got hot water to the valve

I had to part drain down the system in order to change the hot water zone valve body only (not actuator head). On refilling the system, I could not get the hot water circuit back again due to either an airlock or blockage. Despite several attempts to rectify it, the hot circuit is still not working !

 

[Monkey Wrench]

Has the cylinder got water in it by that I mean have you checked the ball valve for sticking

Yes, the cylinder is definitely full of water.

 

[Coldfeed]

I had to part drain down the system in order to change the hot water zone valve body only (not actuator head). On refilling the system, I could not get the hot water circuit back again due to either an airlock or blockage. Despite several attempts to rectify it, the hot circuit is still not working !

So only cold water out of the hot tap? And is there hot water on the flow to the coil up to the motorised valve? If so have you tried manually opening the valve

 

[Monkey Wrench]

Just to update, I received a text from the customer last Thursday morning to advise that they now had hot water and everything was working ok so it seems the "airlock" finally shifted to the loft and out of the vent.

Thank you for all the helpful advice.

 

[oldhand]

Nearly every problem with gravity systems is caused by air locks. Have you tried forcing mains pressure water up the drain cock using a hose ?