Drain down hot water pipe

[TryAgain1]

I'm looking to drain down my hot water (tap) pipe before replacing 15mm with 22mm hot water pipe. I have added a 15mm drain valve to my cold water pipe and plan to do the same to my hot water pipe. This is to stop, after I turn the boiler off and cut the hot water (tap) pipe from leaking torrents of water. My boiler has a 15mm copper hot water tail. Can I add a 15mm drain valve (compression copper fitting) 2m or more from the boiler? I DON'T want to isolate an existing valve (if it exists) on the boiler itself.

 

[terryplumb]

Why are you changing the hot water pipe from 15mm to 22mm , it sounds like you have a combi boiler,is that so ?

 

[TryAgain1]

Why are you changing the hot water pipe from 15mm to 22mm , it sounds like you have a combi boiler,is that so ?

Why? Because 1) there is a long stretch of about 15m from front to back, 2) I think there is a pressure loss and the original hot water pipe is 15mm copper which, despite lagging, still delivers a lukewarm bath and 3) There are more properties being build nearby which is straining an already overused mains water system and we get occasional periods of low water pressure.

So I thought to upside the pipe to 22mm hep2o which is fully lagged. And same for the cold water.

Yes I have a oil combi boiler which I'm sure has drain valve for cold water/hot water/radiator flow and radiator return but, as I'm a DIY'er (despite having a mech eng degree!) I don't want to mess about with the boiler because I might accidentally mess something up!

So I thought adding a hot water drain valve to allow me to drain down the hot water pipework prior to cutting into the pipework and increasing the pipe size from 15 go 22mm. I added a drain valve for the cold water incoming mains and, after isolating the mains stop tap, there was at least 15 litres of trapped water that drained from the drain valve. So I need to install a 15mm hot water drain valve as I really don't want, even after turning off the boiler, to risk 15 litres of lukewarm water flooding the floor/plaster.

Hope that makes sense? I was thinking of using compression copper fittings as the 22mm hot water is copper with tectite fittings.

 

[terryplumb]

Changing the pipework diameter to 22mm will have no effect whatsoever on the hot water pressure. At the length of 15metres that you told us ,that would leave a larger volume of water cooling in the 22 mm pipework,than there currently would be in the 15mm, all of which would need to be displaced before hot water from the boiler reaches an opened tap.
With regard to a drain cock on the hot water pipework,that's fine ,it would of course need to be on the lowest point.
If your combi boiler is delivering only lukewarm water ,you need to establish why. Are all hot taps like this or just the bath taps ?

 

[TryAgain1]

Changing the pipework diameter to 22mm will have no effect whatsoever on the hot water pressure. At the length of 15metres that you told us ,that would leave a larger volume of water cooling in the 22 mm pipework,than there currently would be in the 15mm, all of which would need to be displaced before hot water from the boiler reaches an opened tap.
With regard to a drain cock on the hot water pipework,that's fine ,it would of course need to be on the lowest point.
If your combi boiler is delivering only lukewarm water ,you need to establish why. Are all hot taps like this or just the bath taps ?

The lowest point available for a 15mm drain valve is in the garage which is below the property. The boiler is in the garage sat on concrete floor. When the boiler is turned off, as the outlet water pressure is between 1.5 to 2.5 bar when the boiler is off, I think the pressure should be 1.5-2.5 bar. Is that right?

Most of the radiator pipework and about 1/5 of the water pipework is hep2o plastic. The manufacturer's instructions says that hep2o pipework should not be kept above 70 degrees C. So I'm not sure it's a good idea to keep the outlet water temperature above 70 degrees C same for the radiator pipework.

The only noticeable location where hot water from a tap is not hot enough is in the bathroom - but this bathroom has a hole under the bathtub which leaks heat from the bathtub and cools the hot water very quickly. The bathroom floor is not insulated and is only 1 of 2 rooms that does not have underfloor insulation. Decision logic was 'why not' as I had spare pipework going. And yes I am planning to fill the hole in the floor and insulate under the floorboards.

I installed the 22mm hep2o cold water/hot water pipework some months ago with the eventual plan to connect up to the rest of the 22mm hep2o pipework later on. Surely the 22mm plastic pipework should retain heat better than 15mm copper?

 

[terryplumb]

Are you referring to static or dynamic pressure,when quoting 1.5 to 2.5 bar ?
And how / where are you measuring it ?
As said already ,you need to establish why your boiler is only providing lukewarm hot water to the bath taps, that has nothing to do with copper or plastic pipes being used.

 

[foxhole]

No point insulating under floor , bath needs lagging assuming it’s a steel bath , or would be pointless for a plastic bath .
What temp is your hot water set?
As Terry mentioned your logic is flawed so therefor so is your solution.

 

[TryAgain1]

Are you referring to static or dynamic pressure,when quoting 1.5 to 2.5 bar ?
And how / where are you measuring it ?
As said already ,you need to establish why your boiler is only providing lukewarm hot water to the bath taps, that has nothing to do with copper or plastic pipes being used.

The analogue pressure gauge on the boiler itself which only displays the radiator flow/return pressure. Don't know if static or dynamic. Probably static.

I said previously that I turn down the hot water outlet temperature to a setting of 4/7 (boiler outlet temperature about 65oC) because of concerns over the longevity of the hep2o plastic pipework when subjected to temperatures of 70oC or above. That's the reason why. Does plastic pipework (including the rubber fittings) last when at temperature of 70oC or above? Do you know?

 

[TryAgain1]

No point insulating under floor , bath needs lagging assuming it’s a steel bath , or would be pointless for a plastic bath .
What temp is your hot water set?
As Terry mentioned your logic is flawed so therefor so is your solution.

How does underfloor insulation not improve heat retention in the hot water of the above floor bathtub? The whole point of insulation is to keep heat in. And there is a 0.5m2 hole under the bathtub because of poor installation which suck heat out of air below the metal bathtub.

The boiler hot water is set at 65oC.

What is your suggestion?

 

[foxhole]

Insulation needs to be in contact with bath , once you have an air gap heat is lost quickly .
Pack the underside completely with rockwool .
(A hole cannot suck heat away , ludicrous conclusion .)

 

[TryAgain1]

Insulation needs to be in contact with bath , once you have an air gap heat is lost quickly .
Pack the underside completely with rockwool .
(A hole cannot suck heat away , ludicrous conclusion .)

Yes the insulation needs to be in in contact with the underside of the bathtub. Rockwool is fine I can use insulation netting to retain heat. Have you used rockwool on the underside of bathtubs to retain heat?

 

[foxhole]

You don’t need netting, fill the void .

 

[TryAgain1]

You don’t need netting, fill the void .

Literally shove insulation under the bathtub leaving no gap? I have spare roofing breathable membrane which I think I should envelop the rockwool that I would shove under the bathtub to allow me to easily get the insulation out if needed

 

[terryplumb]

You could fill the whole room with rockwool ,how is that going to result in water coming out the taps hotter than the " lukewarm" that you currently told us about ?
The boilers pressure gauge has nothing whatsoever to do with the domestic hot water. It indicates the pressure in the sealed heating system.

 

[gas112]

As per terry changing to 22mm will make it worse