My googling skills don’t appear to be yielding much…
We have a solid fuel Stove with a back boiler which does the heating and hot water and an immersion heater for hot water only.
Yesterday I made a hole in the return pipe from the stove and had to cut out and replace a wee bit. There was then nothing coming out of the hot taps. I cleared the airlock and water then flowed.
We had the immersion heater on today. The pipe at the top of the cylinder is hot and one half way up is warm but the water coming out of the hot taps is stone cold.
What should I do?
Thanks 🙂

Call a plumber to identify your possible issue and ask them to explain how it works, was my immediate thought from reading your OP.

That’s as practical as I can get with this one.

Too many unknowns about how it’s all plumber together to offer any advice really.

I had similar with my back boiler,I could bleed my radiator circuit no problem,but bleeding my circuit for the water tank proved nigh on impossible, in the end I cut the pipe and installed a water pump so I could pump the water round and bleed it through the pump. Worked a treat. May not be possible on your case.

Double post

Hmm, interesting Mr Pepper. Where did you put the pump and what kind, CH or shower pump for example? Did you just run it when bleeding or did you use it more generally?

An airlock can result in no water but I can’t see how it can result in cold water instead of hot. I would look for possible bridging points between the hot and cold systems. I had a shower mixer with a worn cartridge that allowed flow from hot to cold – when there was equal pressure on both sides, nothing happened, but if the hot was off, the cold water reverse fed into the hot pipes.

Failing that, work out where all your pipes go and draw a detailed map, including height. The problem may become obvious.

if the water coming through the hot tap is the same flow as before, only cold. then it is not an air lock. more sinister forces are at work. Have you a secondary return, or temprature valve anywhere on the system?

Primatic cylinder?

Greybeard may have cracked it. When I run the hot taps the cold water tank starts to refill immediately. What would normally happen is that the hot water would come of the cylinder, which would then refill from the cold water tank, wish I had paid more attention previously so to how long i would take before the cold tank would start to refill and how vigerously it would do this. It sounds very similar to what it does when I run the cold taps in the bathroom.
So, where should I look for this ‘bridge’ and what would it look like?
Actually, reading your post again, I have a mixer shower with mains pressure cold and gravity fed hot, is that a likely suspect, the cold forcing it’s way back up and through the hot pipes without letting any hot water out of the cylinder, leading to cold coming out of the hot taps? Sounds like the sinister forces Lee is on about. Should I put the immersion on, close off the isolators to the shower and then run hot taps and see what comes out?
No idea if it’s Primatic or not, will get the make when I get home and google it.
Wish me luck.
Thanks again chaps 🙂

Should I put the immersion on, close off the isolators to the shower and then run hot taps and see what comes out?

That’s what I would do. Since you have mains cold and gravity hot there’s a good chance the cold will push through if it has any opportunity. If nothing comes out, you still have an airlock to find – in fact, you probably do, because something is still making it behave differently to before anything happened. If you can work out where the pipes go, you might be able to work out a sequence of tap opening to use your accidental cross-link to fill the airlock!

Thanks. I’ll have a go when I get home. If that is the issue then I’ll stick a non-return valve on the shower hot to prevent a reoccurance.

The cold tank would refill immediately you open a hot tap, it works by displacement.
If you’ve got water going across a mixer it will fill the cold water storage cistern and cause it to overflow probably, and likely to happen overnight when there has been no water used.
Make sure no one is using any water and observe the water level in the CWSC, you will probably see it rise.
To have no hot water must be quite a big hole in the mixer.
And I can’t think of many showers that would work with mains pressure on one side and low pressure on the other.

And I can’t think of many showers that would work with mains pressure on one side and low pressure on the other.

That’s another story… Worked OK until this little episode but looking at pumps for the hot water.
Tried closing down the shower but it’s not helped.
The cwsc is only filling when a tap is open,the mains isn’t forcing it’s way up there.
What should I try next?
Or is anyone here a plumber near Galashiels and fancies a small job? Quite near Glentress/Innerliethen if anyone is passing? Not long moved here so no idea who is local and any good, would just be picking a name at random from the Google if I summoned a professional.

OK, new idea required. Note, IANAP (and I think Bear is). If the cwsc if filling when you open a hot tap, the water is being drawn from the hot system. Which should come from the top of the tank, if you only have an immersion. But you have an immersion and a back boiler, so they both feed into the system (I don’t know how it’s done). Is the stove on? If not, possibly you still have an airlock in the line from the immersion, so that the ‘hot’ water is going through the back boiler. If the stove and the immersion are both on, then the water is somehow bypassing them. I would be a bit concerned at running the stove unless you know the back boiler is full and water can circulate, as you don’t want it actually boiling.

Had it before on a bar mixer shower. But both sides on mains pressure.

Try running the hot tap away from the bathroom. Then go to tge suspected bar shower listen to see if you can hear water running through the valve and also feel the valve as it should feel cold to the touch.

If it is that, the hot water is still being drawn from the cylinder but its being mixed down by the cold water that much it comes out cold.

Had it before on a bar mixer shower. But both sides on mains pressure.

Try running the hot tap away from the bathroom. Then go to tge suspected bar shower listen to see if you can hear water running through the valve and also feel the valve as it should feel cold to the touch.

If it is that, the hot water is still being drawn from the cylinder but its being mixed down by the cold water that much it comes out cold.

Had it before on a bar mixer shower. But both sides on mains pressure.

Try running the hot tap away from the bathroom. Then go to tge suspected bar shower listen to see if you can hear water running through the valve and also feel the valve as it should feel cold to the touch.

If it is that, the hot water is still being drawn from the cylinder but its being mixed down by the cold water that much it comes out cold.

When you said it was airlocked, do you mean now water coming from the taps?

I think Bear could be onto something with a primatic, especially if you’ve back filled to hot with mains cold to clear the airlock, there’s a chance you’ve also cleared the air bubble in the tank as well.

edit: You should be able to tell if there is only one big tank feeding it.

To remake the airgap, you need to drain and refill it.

It’s looking likely.
Not sure there are many left, but obviously still a few about. You might struggle to find someone who knows what he’s looking at or is prepared to work out what it is and how it works.

Hello again,

Still no luck, so report on my latest findings:
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The tank looks very much like the one in Paul’s picture and as described by Bear, at least on the on the outside, no idea what it looks like on the inside. The cold in/hot out, stove flow and return and the immersion heater are all in the same layout.
However, Bear seems to imply that this is an older design. This was installed new in November 2015, although it may have been old stock which the plumbers had (Thermaheat of Kelso, bunch of cowboys who wrecked every single floorboard they could get their hands on and a caused a whole catalougue of issues, not ever having them back in the house, hence trying this myself) Anyway, the cylinder is a Telford copper indirect, grade 3, one of these http://www.builderdepot.co.uk/telford-indirect-insulated-grade-3-cylinder-part-l-900-x-450.html None of my googling has told me anything about it being primatic, so I guess it’s not?
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Anyway, I drained the system down again just in case Bear and Paul were right. When I let it refill I again got nothing at all from the hot taps, so back-filled (using the mains cold at the kitchen mixer tap) and now have a good supply of cold water from the hot taps.
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Next, I thought I’d see if I had the same problem as Flux. I can isolate the show completely, but doing this has made no difference.
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I thought I would check how full the hot water cylinder was. Starting to unscrew the immersion heater, about 3″ below the top, causes water to start coming out immediately, implying that it is indeed full.
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I then chucked a bottle of blue food colouring into the cold water tank. The hot taps ran blue pretty much straight away. This tells me that the water is coming straight from that tank and not via the hot cylinder, I would expect it to have taken much longer to have turned blue in that case, and that there is no ‘cold bridge’ to a mains cold supply as that should only give me clean water?
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I hate admitting defeat and calling a professional but I guess I might have to (are you local Bear?)
Going to try Greybeard’s suggestion and draw a map of everything but there are so many hidden pipes I don’t know how possible this will be, I’ll give it a go.
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Thanks again everyone.

Sadly not local.
An indirect cylinder is not a primatic
Is the gate valve on the cold feed to the cylinder turned on?

As you say, your blue colour test is showing that the water is from the cold tank not direct from the main. If the water in the cylinder is hot (top of cylinder and pipe from very top are hot) I don’t see how the cold water can get to the hot taps.

That cylinder you linked doesn’t look primatic to me. Some useful stuff on primatics here which will hopefully enable you to be confident you don’t have one.

I realise looking at the cylinder that my post above regarding the combination of immersion and boiler is bollocks, sorry. That cylinder is for an indirect system, the boiler is the primary circuit and circulates hot water through the coil in the cylinder, so the water in the main part is heated either by the hot coil, the immersion or both, and delivered out of the top of the cylinder – that’s the secondary system, fed from the cold tank.

So the pipe you replaced in your OP is the primary, which should have it’s own expansion tank in the loft. There should be no connection between primary and secondary (except with primatic), each has to fill separately and either could have airlocks if the pipes haven’t been routed well. The primary may have a pump (since you haven’t mentioned it I assume it doesn’t run central heating).

I think the gate valve is turned on. I’m definately turning it the right way, there’s an arrow on it, but it only goes a quarter turn before it stops (red wheel thingy) I haven’t tried forcing it and making it turn more in case I damage it, should it turn more? It’s only a half a turn for the isolators on the shower\tap pipes, turning another half opens them up again. In the panic of shutting everything down in the middle of a water leak I have no idea how much I turned it to turn it off, but that’s how much it seems to open again. I played with one in the shop when I bought the connector to repair the pipe and it turned a lot more but was a different design, couldn’t see one like mine.
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The pipe I replaced is indeed the primary, labled stove F, which I assume is the flow. It comes from the stove, branches and goes in near the top of the cylinder and then does indeed continue up and become the vent.
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The top of the pipe and the cylinder do get hot. This is only from the immersion, I’ve not lit the fire as I’ve read that lighting a fire with an empty back-bolier is a bad idea, not sure how I can verify i there is water in that part of the system?
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The stove does do the central heating too, I can’t see anywhere where this links into the normal hot/cold water, I would expect a header tank but can’t see that this is linked in anywhere. No radiators (one upstairs, three downstairs) have any air in them so I assume this is fine. The central heating has a pump but this has nothing to do with the hot water supply. Without the pump we can have the fire, hot water and upstairs radiator on, with the pump switched on the three downstairs radiators come on too.
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I’ve made a diagram of the mains/cold/hot water system but I’m buggered if I can upload it, photobucket seems to have gone weird since i last used it to post a picture of an old David Brown self-propelled plough in the Tractor Trumps thread.

Dark blue is mains, light blue is non-mains cold and red is, surprise, surprise, hot 🙂
And here’s the plough in case anyone wants that too:

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Hmm. Try this https://www.flickr.com/photos/78177815@N07/shares/448ie5

Photobucket have changed their rules and don’t let you link to the pics from anywhere else. Flickr haven’t and I can see your diagram.

The hot feed from the stove should feed the bottom of the coil, the water rises through the coil and gives it’s heat to the water in the cylinder, then the top of the coil returns cooler water back to the stove. So your diagram has them the wrong way round, but the pipes will be the right way, and I don’t see that it matters to the problem anyway as the stove is off. The CH will be a loop in parallel to the primary HW loop.

The gate valve should turn more than 1/4 turn, it’s a threaded shaft that lifts a spade out of the flow (the isolators are a ball with a hole through that is lined up to the flow or across it). But a gate valve that’s open (say) 1/10 of the way can still let half the full flow through. Try closing it completely and see if you still get cold water from the hot taps? If you do, there must be a cross feed somewhere.

Are you certain you isolated both the shower pipes, and not something else nearby? It’s unusual to feed a shower from mains and tank-fed hot; I had one that was fed from the hot and a separate cold feed from the same tank, a cross feed in such a thing would explain the blue colour getting through. No mixer taps anywhere else, like the bath?

Point of note if it is a gravity flow to the cylinder it goes to the top of the coil. So the diagram is correct.

As mentioned if it is a gate valve it should move several revolutions to turn off or on. Try it either way. They are great at getting stuck or even shearing in either the open or closed position.

If your dye test was as immediate as you say then somewhere it is going across from low pressure cold to hot. Look for the only places that can be and isolate if possible. But first I would be checking that gate valve……

Went back to the gate valve. Turned it, it stopped. I held my breath and gave it am almighty heave. It went bang in very disconcerting way that seemed to reverberate through every single pipe. I turned again and it did about three complete revolutions.
I went downstairs and turned on the hot tap. It gurgled, spluttered and produced hot water 😀
You are all marvelous but especially Bear and Greybeard. Thankyou all very much
Still can’t believe I’ve spent a week buggering about with a valve which wasn’t open!

Great result!

No probs, glad you’re sorted.