Hot water supply has suddenly become very slow

Naf

ThisIsWeird said:

• The big red wheel is a gate valve, and that suchs off the CWS to the DHWC. It should be FULLY open, and then backed off a half turn closed just to help prevent it from seizing. Does it turn easily?
  

See bits in bold.

In addition, as you say, it would be hard to attach a hose to the top of the DHWC as all the pipes are soldered.

Yeah, turns really easily.

ThisIsWeird

Naf said:

ThisIsWeird said:

And please confirm that ALL the hot taps are affected? ALL!

Yes indeed. Current state of affairs is absolutely no water coming from the balanced cold supply; and we reckon about half of the usual from all the hot taps after it settles.

Could you clarify this point, please? There is currently what coming from what?

ThisIsWeird

And, I presume there are two supply pipes coming from the near-bottom of the CWS, one to supply the DHWC, and the other is the cold feed to the taps (other than the kitchen). Yes? And that cold feed also has a gate valve on it? And it's also fully open? 
You haven't had a plumber doing work recently?

Le_Kirk

Naf said:

ThisIsWeird said:

• The big red wheel is a gate valve, and that suchs shuts off the CWS to the DHWC. It should be FULLY open, and then backed off a half turn closed just to help prevent it from seizing. Does it turn easily?
  

See bits in bold.

In addition, as you say, it would be hard to attach a hose to the top of the DHWC as all the pipes are soldered.

Yeah, turns really easily.

I would expect some resistance; I've never known a gate valve to turn really easily; maybe it has rounded off and is not actually turning the valve stem!

Naf

ThisIsWeird said:

Naf said:

ThisIsWeird said:

And please confirm that ALL the hot taps are affected? ALL!

Yes indeed. Current state of affairs is absolutely no water coming from the balanced cold supply; and we reckon about half of the usual from all the hot taps after it settles.

Could you clarify this point, please? There is currently what coming from what?

The cold tap on the bath/shower which is fed from the CWS isn't flowing at all anymore. Pretty sure this is an airlock, so I'll be firing some mains pressure back up it with the tap adapters I bought today.

All 3 hot taps are flowing a little. When they're first opened after a little time closed the flow looks good, then it quickly drops and ends up looking about half what it used to be before these problems started.

Naf

ThisIsWeird said:

And, I presume there are two supply pipes coming from the near-bottom of the CWS, one to supply the DHWC, and the other is the cold feed to the taps (other than the kitchen). Yes? And that cold feed also has a gate valve on it? And it's also fully open? 
You haven't had a plumber doing work recently?

Yes, two supplies. One we added just a couple of years ago as we got fed up with the shower being so difficult to balance when it's cold was fed from a partially gated mains.  Yes gated, yes open.

But no work in probably about a year.

Naf

Le_Kirk said:

Naf said:

ThisIsWeird said:

• The big red wheel is a gate valve, and that suchs shuts off the CWS to the DHWC. It should be FULLY open, and then backed off a half turn closed just to help prevent it from seizing. Does it turn easily?
  

See bits in bold.

In addition, as you say, it would be hard to attach a hose to the top of the DHWC as all the pipes are soldered.

Yeah, turns really easily.

I would expect some resistance; I've never known a gate valve to turn really easily; maybe it has rounded off and is not actually turning the valve stem!

It doesn't spin like a bearing or anything, but there's no struggle to get it to shift. If I have a tap running and turn it off and on I can hear the flow stop and start back up

FreeBear

A sink plunger over the outlet pipe in the CWS tank might clear a blockage or air lock. Will stir up the crud in the bottom of the tank though.

Naf

FreeBear said:

A sink plunger over the outlet pipe in the CWS tank might clear a blockage or air lock. Will stir up the crud in the bottom of the tank though.

Yeah, I did have a go but it's very difficult to get a decent seal around either of the outlets due to their positions.

ThisIsWeird

Naf said:

The cold tap on the bath/shower which is fed from the CWS isn't flowing at all anymore. Pretty sure this is an airlock, so I'll be firing some mains pressure back up it with the tap adapters I bought today.

All 3 hot taps are flowing a little. When they're first opened after a little time closed the flow looks good, then it quickly drops and ends up looking about half what it used to be before these problems started.

Thanks. And the basin cold is similar? (Assuming both are supplied from the CWS - or is the basin still 'mains'?)

It is astonishing that both the H and C supplies are so prone to air locks, assuming that the dedicated cold supply from the CWS to the bathroom is a far simpler route? Can you trace that pipe run? Again, any long horizontal lengths, or upwards sections?

"so I'll be firing some mains pressure back up it with the tap adapters I bought today." Oookkkaaayyy, so you are going to cobble together a length of hose, with a controllable valve on it, leading to a tap adapter that'll fit over the miscreant hot and cold spouts? Ok, absolutely ensure that the gate valves are fully open (ie, all the way, then closed a half-turn - which makes no difference to the flow), especially the one supplying the DHWC. 

Have someone at the CWS observing what's going on as you turn on the hose flow up t'hot spout gradually. You'll want to see evidence of water backflow into the bottom of the CWS - perhaps a slight disturbance of the sediment on the bottom, or a swirling, or just the water level slowly rising. And, ideally, some bubbles!

Perhaps do the cold tap first, as this is more straight-forward and should be a good trial run.

When doing the hot, then especially turn on the mains gradually, as you don't want to 'shock' the thin-walled hot cylinder. The person at the CWS should observe whether the ejected water is coming out the bottom of the CWS or the expansion pipe over it!

If the hose is long enough, you could alternatively do this from the CWS end - stick the hose into the bottom tank connector holes as far as possible - they should fit - and open the hose valve. Again, don't 'shock' the DHWC, but turn up gradually. Obviously, the actual taps must be fully open, but keep the plug in the basin or bath to see if any debris comes out.

Hopefully this will work ok, as it does all sound like airlocks. Is the CWS mounted as high as it can be, or could it be easily raised a couple of feet or so? That would increase the flow pressure, and make a repeat less likely - as well as providing a generally better flow rate.