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.

 

[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 ?