Draining hot water pipes

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Hi,

I'm a competent DIYer and i am working on my brothers new house - i need to re do the plumbing in the kitchen (hot and cold taps) and also renew the pipework in the bathroom to fit isolation valves to the hot and cold tap (currently a direct pipe to tap).

He has an indirect heating system - a water tank in the loft, immersion heater in airing cupboard, and a boiler in the kitchen downstairs. i've never worked with this system before.

My plan of attack is this:

1. turn off stop tap in kitchen, and turn on all cold taps to drain cold feed pipework
2. Turn off the heating system - boiler in kitchen and immersion heater in airing cupboard
3. Do i need to lift up / isolate the ballcock in water storage tank in loft?
3. Turn off the red gate valve on the pipe that comes from the cold water tank in the loft, down into the bottom of the immersion heater.
4. Once i've turned off this gate valve, do i need to turn off any other valves before i turn on the hot water taps to drain the pipes.

Just to make it clear, i only want to drain the hot feed that supplies the taps, not drain the boiler system / immersion tank.

I assume that once pipework is done, it should be a simple case of opening the valve and he whole system should be working again?

Please may someone advise if i'm along the correct line of thinking?

Thank you.
 
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If you turn off the gate valve into the cylinder then turn on hot taps the system will drain as far as the draw off from the top of the cylinder, a rush at first then stopping after a short time.
 
If you turn off the gate valve into the cylinder then turn on hot taps the system will drain as far as the draw off from the top of the cylinder, a rush at first then stopping after a short time.
thanks for your reply. so effectively i need to turn the gate valve off and turn the taps on until water runs dry, and then i can carry out the pipework and reopen the valve? Thanks
 
Yes, do the other things like turning off the heating system , you should not need to tie up the ball cock if the gate valve is working OK.
Gate valves often let by a little water so be prepared with some towels to cope with any dribbles.
 
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Be aware that you're relying on a manometric vacuum which "holds up" all the water in the tank. If air gets into that 'bubble' then all the wate will flow out, or until the incoming air is prevented getting in. The reality of this is if you're cutting a pipe somewhere, this might allow the air in and 200 litres of water might come flooding out with no way to stop it as you put a slit in a pipe.

Optionally, open a hot tap elsewhere and therefore intentionally allowing as much water as possible to flow out to minimise what might otherwise come you way. When returning to service, be aware the hot taps will clunk and spit as the air is pushed out. This water hammer effect could be quite dramatic if you try to do it too quickly.

Nozzle
 
okay thanks. so as i'm working on the pipes in the upstairs toilet (sink and toilet in separate room to bath) and also the pipes in the kitchen downstairs, should i first of all shut the gate valve in the airing cupboard and then keep the hot tap turned on in the BATH while working on the pipes in the kitchen and toilet.

it should only be a very short period of time as i'm using push fit isolation valves directly onto the cut pipe, so i can quickly fit them once cut.
 
Close the valve on the cold feed to the bottom of the hot water cylinder ,as already advised, and turn on all hot water taps ,including the one on kitchen sink. If hot water does not cease to flow after 5 mins ,the valve is not fully closing ,and that is a common problem with gate valves , which also fail to open when you want them to. Especially if you overtighten them when closing them as they snap inside !!
 
If it's an old gate valve, be careful, they have a habit of seizing/jamming up if over tighten and then they can snap. work the tap back and forward a good few times before you try to tighten it down fully, don't overtighten or it could jam.
 
Turn off the incoming stopcock and open all taps until water has stopped, remove any gate valves leading from the cold water storage tank and fit full bore lever valves. This includes the one leading to the hot water cylinder. Then fit any isolation valves to basin/toilet and kitchen pipe work, I would advise fitting full bore isolation valves.

https://www.screwfix.com/p/pegler-ball-valve-blue-22mm/18343

https://www.screwfix.com/p/pegler-ball-valve-red-22mm/45277

https://www.screwfix.com/p/full-bore-isolating-valve-15mm/46860

Andy
 
Turn off the incoming stopcock and open all taps until water has stopped, remove any gate valves leading from the cold water storage tank and fit full bore lever valves. This includes the one leading to the hot water cylinder. Then fit any isolation valves to basin/toilet and kitchen pipe work, I would advise fitting full bore isolation valves.

https://www.screwfix.com/p/pegler-ball-valve-blue-22mm/18343

https://www.screwfix.com/p/pegler-ball-valve-red-22mm/45277

https://www.screwfix.com/p/full-bore-isolating-valve-15mm/46860

Andy
thank you

so by turning off the main stop tap (in kitchen) and opening all taps in the house, will this drain ALL water in the house - ie. cold water storage in loft, all pipework, the immersion heater? I assume i need to turn the boiler off before doing this?

Cheers
 
It will drain all except the hot water cylinder ,which will remain full of water but no more will come out of it once hot taps run dry. Of course your central heating will not be drained !!!
It will also waste a lot of water as the loft tank will be emptied.
 
Last edited:
ok, thanks all for your input. So to get things cleared up, lets assume i want to:

- replace the gate valve on the cold feed from loft into bottom of heater (which doesn't seem to move as it happens
- replace / renew new pipework in kitchen for hold and cold supply
- cut hot / cold feed pipes in toilet for sink, and install new isolation valves

so effectively, all i need to do is turn off the stop tap where the mains come into house, turn on all hot and cold taps until water runs dry.

Replace gate valve, kitchen pipework etc and then turn mains stop back on, and will the system automatically return back to normal?

Do i need to turn the boiler off or not, before carrying out this work? I obviously don't want to mess up the heating system.

Cheers
 
Turn off electric supply to boiler.
If gate valve on cold supply to hot water cylinder is located above the take off point for hot water ( from the top of the cylinder) ,then everything you stated above is correct.
Bear in mind that there will always be certain pipes that contain some water , especially those on lower levels that are below tap outlets.
One thing you may encounter when turning mains back on ,filling loft tank etc ,is air locks on the gravity fed pipework .
Before fitting taps / toilet / showers etc. Flush all pipework from the localised isolation valves.
 
Last edited:
Turn off electric supply to boiler.
If gate valve on cold supply to hot water cylinder is located above the take off point for hot water ( from the top of the cylinder) ,then everything you stated above is correct.
Bear in mind that there will always be certain pipes that contain some water , especially those on lower levels that are below tap outlets.
One thing you may encounter when turning mains back on ,filling loft tank etc ,is air locks on the gravity fed pipework .
Before fitting taps / toilet / showers etc. Flush all pipework from the localised isolation valves.

thanks for your reply! Sorry to come across a bit thick - when you say "flush all pipework from the localised isolation valves" do you mean put water into the top of them so the water goes into the pipework?
 

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