I need to fix a leaking hot tap downstairs and we have an indirect unvented system (well we have no tanks in the loft, and a Megaflo in the airing cupboard).
I've been reading up this evening on how the system works and, indeed, the system's correct nomenclature.
To fix the tap I need to drain the hot water and I'm not exactly sure on what I'm going to do so I thought I would run it past this forum first. Here's my plan:
1. Switch off heat source (boiler in kitchen)
2. Switch off the cold water supply to the Megaflo (there's a lever on the pipe feeding into the base of the tank rather than a red-tapped type valve)
3. Open the cold taps (not in the mains fed kitchen) to drain the storage cistern/tank.
4. Once the cold taps have run dry open the hot taps to drain pipes and partially drain the hot water cylinder
5. Repair tap
6. Close all open taps
7. Resupply cold water to cistern/tank
How does this all sound? I've read that I can drain the tank from a drain valve (and hose) at the cold water inlet, but using the taps sounds more practical!
Why are you wanting to drain it? Unvented systems are all at mains pressure. There will be a lever (probably) valve somewhere near the tank that will isolate it and thus shut off BOTH hot and cold supplies.
All you have to do then is open the tap you wish to replace, allow only the pipework that feeds it to drain, do the replacement and then open the isolating valve again.
I have a similar set up on a newly installed hot water system, although I only have an isolating valve on the cold water supply pipe t the hot water. This means that when I want to work on a hot water tap I will need to drain the tank. The first time I do this I will be fitting an isolating valve on the hot water outlet from the tank too. Could someone please advise if I risk getting an airlock in the tank (it is in the loft at the top of the system) or if the system should be set up to release air from the tank.
If I do risk getting an airlock will there be a bleed valve on the tank or is there another way to let the air out?
Don't worry about getting an air lock, especialy on the hot water side, they are very rare on pressurised systems, if it does for some reason airlock then let the air out oft he temperature pressure relief valve on the side of the cylinder
As usual with these sort of projects it's the bits you don't think about that turn out to prevent you from easily completing the job!
Turning the water off was the easy bit. Turned water heating off, shut cold water feed to MegaFlo, turned on downstairs tap that I was repairing, and about a teacup of water came out and that was it. All ready for the repair...
Took the head off the tap, but couldn't release the headgear. Several doses of WD40 and some waiting time later I ended up removing the tap from the basin to allow me better access...inevitably I ended up rounding the nut off.
Off to Wickes then and eventually, four hours after starting (allowing for lunch of course), I have replaced two taps. I hope my re-tightening stays OK.
The cold tap was isolated just by turning off the mains feed under the kitchen sink. When it came to turning on the cold feed to the MegaFlo I got the other half to stand by the hot tap downstairs checking it wasn't spitting out everywhere. At time of writing the boiler's on and a bath has been run...and I have a working, spare cold tap should I need one!
Cheers again everyone! For the desperately sad I have blogged my story, complete with photos...
Google "jonnyandtracy.com" and search for replacing a tap washer
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