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.