Megaflo balanced cold water question

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Guys, just installing 2 thermostatic showers on an existing megaflo installation on a property I have just purchased. I believe it is advantageous to have a balanced cold water feed to the 2 showers. This can be achieved by me taking the cold water feed to the 2 showers after the cold water combination valve. My CWCV is located within 1 foot of my megaflo. My question is in the installation manual it states that the "tapping should be at least 3m from the megflo inlet connection". Am I correct it assuming they mean the inlet at the bottom of the megaflo, if so then I can achieve this 3m distance by creating a loop of 22mm copper within the airing cupboard between my CWCV and the inlet of the cylinder and then branching off from this(closest to the CWCV) towards the showers (these are located on the other side of the airing cupboard so are closer than 3m if I were to pipe directly. Thus I will have my showers approx 1.5 m & 3 m from the CWCV and they will be 4.5 & 6M from the inlet at the bottom of my Megaflo. PS is the 3m distance to do with the potential of the megaflo heating the cold water towards the mixer valves.

Hopefully you get my drift! Thanks a lot

 
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The pressure reducing valve usually has a seperate blanked off tapping to feed balanced cold water applications. I dont see that on yours.

Potentially more problematic, yours seems for no reason to have a short length of 15 mm in the supply to the valve.

I dont understand what they have said or what you have said either. Its getting late and they are probably both out of context.

As far as I can see taking a cold from the horizontal section should suffice.

I would be getting rid of all 15 mm in the supply side too.

Tony
 
There's not much point taking off a balanced cold feed if your mains pressure is less when flowing, than the 3 or 3.5 bar pressure reducing valve you have, as they'd be nearly the same anyway. Only if the cold is say 5 bar...

Yes the 15mm isn't ideal but if your showers have hoses, the hot has to share 4 feet of 10mm bore with the cold it's mixed with, so the short 15mm for hot alone, won't make much difference.


What's 3 metres?? :confused: !
 
Yes have already got rid of the 22mm to 15mm reducer that had for some reason been put on the supply side done after taking the photo.

PS pressure is 4.2 bar

Cheers
 
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From where I'm sitting this has never been installed correctly in the first place :eek: I would think this installation has never seen a G3 competent person in its life :rolleyes:

The prime example is the pressure relief valve pipe going upwards.

I would remove the combination valve, extend the 22mm cold pipe up to the top of the cylinder then re-fit the combination valve there.

Then bring down the 22mm balanced cold to the bottom of the cylinder and fit the required drain off.

The discharge pipes must then be fitted as per current G3 regulations, which from what I am guessing, you do not hold, so therefore should not be altering anything to do with this cylinder.
 
ChrisR, just re-read your post (yes it was late last night) and can fully understand what you are saying that there is little point in having it on the balanced side if less the 3 bar when flowing as there is no potential to have the cold feeding in at a greater pressure than the regulator allows on the DHW side. Is this correct if so then I can just take a branch off in the shower rooms from its current feeds.

gas4you thanks for the heads up
 
I would always recommend having balanced feeds to showers because of their sensitivity to differential flow rates.

Also the incoming water pressure can vary widely at different times of day depending on the local demand.

A properly installed unvented will have an adequate supply pipe size which will always have a residual pressure of at least 0.5 bar above the set working pressure for the cylinder.

Unfortunately in London even the static supply pressure is rarely above the set working pressure of the cylinder which is what Chris's comment was based on. Where possible a good installer will reduce the working pressure to a point where some regulation will still be achieved.

Tony
 
Yep, I agree with all the above. Except to point out that you can't alter the PRV pressure on a Megaflo®
The 3 metres is presumably about not getting hot water in your cold outlet pipe. The tee is after the non return valve, so HW could come back up the supply pipe and come out of the cold.
There's a heck of a lot more than 3m of 22mm pipesworth of compressed air in the HW cylinder, so where they get 3m from escapes me at the moment! I suspect they've made a mistook, and calculated for the thermal expansion only, and ignored the bit about the internal air space being at mains pressure until you open a cold tap, at which point it drops right down to the dynamic cold water pressure.

As it goes to a shower and not a drinking water tap I wouldn't worry too much about it.
As your pressure is 4.2 bar then yes use a regulated cold output, though it's probably a lot lower when you turn the tap on.
Even when the pressure is lower, both supplies then come through a similar resistance. Most people use thermostatic shower mixers so it doesn't matter anyway!.
 
From where I'm sitting this has never been installed correctly in the first place :eek: I would think this installation has never seen a G3 competent person in its life :rolleyes:

The prime example is the pressure relief valve pipe going upwards.

I would remove the combination valve, extend the 22mm cold pipe up to the top of the cylinder then re-fit the combination valve there.

Then bring down the 22mm balanced cold to the bottom of the cylinder and fit the required drain off.

The discharge pipes must then be fitted as per current G3 regulations, which from what I am guessing, you do not hold, so therefore should not be altering anything to do with this cylinder.

All agreed, the PRV discharge pipe is the first bit I spotted as well. One wonders where the TPRV is connected, or even if it's connected at all, and looking at the wider shot I'd doubt very much if the PRV is within 500mm of the tundish. There should also really be a drain off where the cold supply enters the cylinder, to allow draining for maintenance. I would strongly advise getting a professional registered installer in to your house at the earliest opportunity to rectify the faults we can see here, and also any that may be there out of shot (will be more than happy to advise if you provide a pic of pipework higher up).
 
Guys I really appreciate your comments and help. Yes it is much nicer to have a drain cock at the bottom of the megaflo and attached is a picture showing the TPRV and siting to the tundish ( it is a straight drop 600mm approx with no bends to under floor then to the outside of the property). Also the PRV on the combination valve no longer has to work uphill. Showers now have a balanced cold feed as well thanks to some new pipework.
 
Cor things move quickly in here. Spoke to heatrae sadia and they reckon I now need a core unit and new expansion valve. I have checked the schematics and believe this may be wrong advice I have looked at the schematics again and believe as long as the take off for the showers is over 3m away and you do not have balanced cold going to drinking water then the way it is plumbed in is fine.

cheers
 

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