hot water system problems

[andyplumber]

hello

long time since i have been on here, wondering if anybody could help me with a problem with a old hot water system on a care home,

the problem i have is no hot water pressure on the second floor, same floor the storage tanks are situated (300 gallons) at least 1 meter head from tap to bottom of tanks

hot water traveling up cold feed and causing tanks to overflow, i have slowed this down by switching off the secondary return but the building now has cold water on ground and first floor, need to run for 5 minutes to receive hot water, ideally need to get the return switch back on asap.

the system has been designed badly, all 40 basins have TMVs as required but not balanced supplies tank fed hot and cold mains water connected to showers and basins i have thought maybe a non return valve is passing and allowing the hot to travel back up the cold feed

i have thought about recommending they change the cylinders to unvented and a accumulator due to low mains pressure (2.5 bar)

any ideas would be a big help, i suppose 2 heads is better than 1

 

[Whyme]

is there not a rogue tap without nrv anywhere ? can only be cold beating the hot like ya say. accumulators are fine but sized to a place like that would be massive. thought about boosted water via a pump set and your unvented?

 

[Whyme]

With new big sectional tank, forgot to say lol

 

[Whyme]

tbh if 300 gallons have served them thus far an accumulator may be a good shout, not like there teenagers standing in the shower washing there troubles away too the smiths..

 

[tamz]

It would take about a shift (or 2 if you spin it out) to find where it is feeding back from.
I don't think i wouldn't necessarily go with unvented (even if they were willing to spend the money) unless you want to sell them the potable water road.
Anyway, just for Gaz
[video=youtube;XbOx8TyvUmI]https://www.youtube.com/watch?v=XbOx8TyvUmI[/video]

 

[snowhead]

hot water traveling up cold feed and causing tanks to overflow,

If the Cold supply for the Hot water originates from the storage tanks it cant be that causing the overflow, water would just be traveling around a loop.

You're getting another source of water into the Hot system.
That's coming from the Mains Cold.

You've got a failed Non return in a TMV or adjacent to it.
It may be that someone else has replaced a TMV recently that doesn't have Non returns built in.

How to isolate the problem;

Turn the Circ pump back on.

Go to each TMV, put your hand on the HOT pipe, open the HOT tap till the water in the pipe is Hot / Warm.
Turn the tap OFF, if the HOT pipe goes Cold straight away you've found a failed / missing Non return.

Go to every TMV there may be more than one.
Also check Prewash Spray mixers in the Kitchens if they have any.
And any other tap where Hot / Cold mix within the tap.