25 bedroom hotel

[J murton]

Hi all

going to look at a hotel with 25 bedrooms tomorrow.
Customer has put the following:

believe that a tmv is allowing cold water to enter the hot system, location unknown. requires diagnosis Bedroom Nº: all.​

what would be best way to test tmv for backflow. How would you go about a job of this size to fault find ?

my idea was potentially using nrv to stop backflow.

many ideas welcome

thanks

 

[snowhead]

Cold is only going to cross over to the Hot if the Cold is H.P or boosted and the Hot isn't.

Gain access to the TMV and the Hot and Cold pipework to it.
With your hand on the Hot pipe, open the tap that the TMV supplies.
Run the tap till the Hot pipe gets hot.
The Hot pipe may be cold to start but will warm up.
Shut the tap, if the Hot suddenly goes cold you've found one of possbily a few or many culprits.
Fit NRV on Hot pipework.

Repeat for every tap, don't assume you fixed it till you've been around all the TMVs.

 

[J murton]

Cold is only going to cross over to the Hot if the Cold is H.P or boosted and the Hot isn't.

Gain access to the TMV and the Hot and Cold pipework to it.
With your hand on the Hot pipe, open the tap that the TMV supplies.
Run the tap till the Hot pipe gets hot.
The Hot pipe may be cold to start but will warm up.
Shut the tap, if the Hot suddenly goes cold you've found one of possbily a few or many culprits.
Fit NRV on Hot pipework.

Repeat for every tap, don't assume you fixed it till you've been around all the TMVs.

Great advice thanks for that will give it a go

 

[ShaunCorbs]

You could also try turning the hot off and opening a hot tap then go round all of them one will be the same temp either side of the tmv might even see condensation

 

[J murton]

Sound advice.

So I’ve been to the site and checked out the situation.

The hot water takes a while to come through which shouldn’t because it’s got a circulation system.

When it does come through I turn the hot off and the pipes cool almost instantly.

I then turned the hot iso off and cold water flows through the tmv and out the hot tap.

so I will change the tmv and check ok. If it does persist then will need to add in a nrv. Pipewo

 

[ShaunCorbs]

Did you try turning the cold off to this tmv ?

 

[J murton]

So I changed the tmv and cold water still getting into the secondary return/hot feed. Having pulled hot water through hand on pipe water comes through hot. As soon as the tap is turned off the pipes go cold within seconds. So mains is entering the hot somewhere. 🤔

 

[ShaunCorbs]

Turn the hot off and then go round turning the cold to the tmv off and checking via hot tap that’s not tmv3 will flow if you haven’t found it

 

[Scott_D]

Is the secondary return piped properly?
Does it go to each bedroom like you have pictured?

 

[J murton]

Is the secondary return piped properly?
Does it go to each bedroom like you have pictured?

Yes goes to each bedroom

 

[Scott_D]

Is there anything to prevent it taking the shortest route then back to the cylinder?

 

[oz-plumber]

Post a pic of the cylinder and the pump installation.

Could be a faulty NRV at the pump outlet or the incoming cold water supply plumbed in incorrectly.

It only takes one incorrect connection or valve at the plant area to have cold water pass into the system loop