No water entering HW cylinder from CW storage

[honestworker]

Conventional system: CW storage in loft, HW copper cylinder in loft below it fed by 22mm pipe that drops vertically (through 22mm gate valve below tank). 22mm pipe drops about an inch below the level of the connection to the cylinder, goes through a 90 degree slow bend and then rises up to the HW cylinder.
Cock-type drain valve in the 22mm pipe close to where it enters the bottom of the HW cylinder.

Had to drain both tanks due to a leak. Repaired leak. Refilled CW storage from mains CW. Airlocks in HW pipework so blew them out using mains CW from a flexible hose under the sink. Mains CW discharged from HW cylinder through vent pipe into the CW storage and then overflowed to outside.

Now have HW from all HW taps but this stops after a while as the HW cylinder is not refilling. Drained HW cylinder using drain cock on 22mm pipe near connection to HW cylinder- drained OK, some discolouration but no sediment. CW storage tank is plastic and clean inside, no obstruction.

Never had an airlock in this house in 30 years. How do I clear an airlock between CW storage tank and HW cylinder? Is it an airlock?

Thanks in advance for any ideas.

 

[oldbuffer]

1. First suspicion would be the gate valve. Either spindle snapped in closed position or blocked.
2. Secondly given that you have reverse flushed it would suspect something is acting as a flap. Check base of cold water storage cistern near exit to hot water cylinder feed for something letting water through in reverse, but not forward.

 

[JohnD]

Good idea. Feel the gate valve. The "spade" part often seizes and snaps off the spindle. The spindle can still push it shut, but can't pull it open.

If you need to replace it, the Pegler ball valve with lever is much better. I expect yours is 22mm

Note the body looks "fat" on the full-bore ones

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[CBW]

Is the float valve working?

 

[honestworker]

Chris - yes, the float valve in the CW storage is working OK - fills up CW from mains CW supply without any issues, then rises and stops CW entering.

 

[Dereekoo]

Turn on hot taps and run a hosepipe up to the header tank and blow it down the outlet it will either flow or blow back at you.

 

[CBW]

Could be sediment or something that's blocking, air lock as you suspect or something else

 

[honestworker]

Thanks, Derekoo. Good idea.
I could disconnect the 15 mm CW supply at the CH header tank, attach a hose to the 15 mm pipe, then stick the hose into the HW 22mm supply outlet at the bottom of the CW storage tank (drain some of it first and tie up the ball valve, so that the freezing cold water comes up only to my elbow!). Good idea to open hot taps first.