Almost no hot water after idiotic mistake

[Jim Hatfield]

I have a traditional vented and fully pumped system. I also have a water softener in the kitchen which sprang a leak from somewhere inaccessible at the back. So I closed the flow and return valves and opened the bypass valve to stop the leak until such time as I could properly get to it.

Except - I didn't check that the bypass valve was really open. It wasn't until I got home from work 24 hours later and SWMBO informed me that we had no water from some of the taps that I realised. The bypass valve was stiff and I had just turned the lever, not the valve.

By the time I had opened it properly the damage was done. I guess both the cold water storage tank and the hot water cylinder had drained. And the shower pump had run dry.

Now we have virtually no hot water (and I think the hot side of the shower pump is shagged).

It has symptoms of an airlock but I can't get it out after days of trying so I think that's not it. I think what has really happened is there is a blockage in the cold feed to the cylinder causing very low flow. At equilibrium the vent pipe is nearly full, so when you open a hot tap you get the contents of the vent pipe then nothing. The shower runs cold unless you turn the mixer to full hot, then it's feeble.

I can live with replacing the shower pump, all the connections are pushfit, but how on earth do I fix the blockage (if that is what it is)? The feed to the cylinder is right at the back of the airing cupboard, a pig to get to, and the drain c*ck is only 1" above the floor.

I have had it suggested that the blockage may be at the top of the cylinder, in the outlet pipe - but that's equally a challenge. The pipe runs horizontally from the coupling at the top of the cylinder to a tee which is only 1/4" away from the wall - I don't think that amount of movement will release the pipe from the coupling, I'll have to move the whole cylinder the other way. I'm really reluctant to do that what with all the other pipework.

Any ideas how I can confirm if it is a blockage and if so where it is likely to be? And where does one buy rubber tube these days, if I need to drain the cylinder I'll probably have to run a tube out of the window and rely on siphoning to empty it, since the bottom of the window is about 3' higher than the drain c*ck.

I hate plumbing....I think I'll go for electric underfloor heating in my next house and hang the running costs...

[Peter Andrews]

Have you tried connecting the cold mains tap to the hot one, at the kitchen sink, and back filling - I have used a piece of cycle innertube for this, this will often shift an airlock. I assume your cold tank is now full; I've also successfully shifted a similar airlock by simply(!) blowing up the hot bath tap.

Peter

[Calvin]

This sounds similar to something I experienced with an older installation, the bottom of the feed pipe was blocked with crud and it happened suddenly, immediately after the cold storage tank had been run dry. My guess is that as the cold tank started to fill up the crud at the bottom was distrurbed and ended up being sucked into the pipe to the hot cylinder. The actual blockage turned out to be in the

90 degree elbow where the feed pipe joins the cylinder but we didn't know that at the time and we ended up replacing the whole pipe run.

It sounds like you *may* be suffering something similar. If that's the case, and given how difficult your access sounds, I'd perhaps try "reverse flushing" it. How about sealing the vent pipe (don't forget to un-seal it again afterwards) then forcing mains pressure water back up a hot tap? One of two things should happen. Either the cold storage tank will backfill via the cylinder meaning that the blockage has cleared (or there never was one) or the cylinder will pressurise to mains pressure.......... I'd take things very slowly and carefully I think!

I can't see how the top of the cylinder would block but I'm willing to be educated.

Plastic tube in many sizes is sold in B and queue or in any pond or fish shop.

Good luck Calvin

[David Hansen]

On Wed, 31 Oct 2007 19:47:27 +0000 someone who may be Jim Hatfield wrote this:-

Which taps, on which floors?

If the pipes are designed and installed properly then the only way to drain the (shell of the) cylinder is to use the drain c*ck at the cylinder. If this was not the case the cylinder remained full.

Drain down the cylinder and the rest of the hot water system. It is important to remember the first bit as a full cylinder contains a lot of water.

People have been known to cut holes in walls to get at such connections. Alternatively it may be easier to remove the whole cylinder, remember to shut off or drain the heating first, complete with some pipework. For example a difficult connection at the back may well become an easier connection higher up if the pipe is cut.

[TheScullster]

"Calvin" wrote

No need to seal the vent and certainly not recommended! The back flush method will work fine without blocking the vent. As others have said, keep an eye on things - particularly water level in the main storage tank, otherwise you are likely to end up testing the tank overflow as well!

Phil

[Jim Hatfield]

Yep, the washing machine supply is both hot and cold, the cold from the mains, so I did that. It was that which convinced me that it wasn't an air lock after all.

[Jim Hatfield]

Didn't think of that - thanks for the suggestion, I will try it.

[Jim Hatfield]

Downstairs loo cold, which comes straight from the softener. All hot taps. And the shower "wasn't working right".

I realised that about an hour after I posted, typically. But it could have drained to the level of the hot feed to the shower pump which is about a foot below the top of the cylinder.

Gulp. What a price to pay for a tiny mistake. Serves me right.

Well most of the connections will come off reasonably easily, but unfortunately the pump and valve are in front of the cylinder, blocking it's way out, so they would have to come out too. I think I will try draining down first, if I can get some hose properly secured on the drain c*ck.

Sounds like a fun weekend ahead....

[edalechurchcottage]

I've just had airlock in the gravity hot water too. Had it once before when the system was drained down.So I fitted a double check valve in the cold mains feed to the washing machine, then its easy peasy to just connect the hot water hose from the washer onto the mains cold.I turn on the cold a little with all the hot taps slighly open, always clears, and after much bubbling as the air is forced into the header tank, Once either the bubbling stops or , a constant flow is coming from the vent , can be pretty sure the air lock has gone.Then I run a tap untill the ball vave opens , then I know the tank level is back to normal

[jgh]

Does any of the pipework from the cylinder cupboard run down through the floor to the room below? In my airing cupboard there's enough wriggle room to feed a hosepipe through the floor to the kitchen sink, thence the cylinder drains to.

-- JGH

[Jim Hatfield]

Thankfully it was nothing like as hard as I had thought to drain the cylinder, and once done and refilled, the problem is gone. Even the shower pump works fine. Thanks to all for advice and suggestions.