)TMV - non-return valve (school)

[maxdani]

We have had an ongoing issue with low hot water temperatures in a school.

During the recent repair of a leak, the plumbers isolated the hot water to fit a new bit of pipework and found that water wouldn't stop running until the cold boosted water was also isolated. Given this, it would seem that the cold water is mixing with the hot.

I believe the most likely cause is the hot water non-return valve failing somewhere. Due to the size of the site, there are approximately 40 TMV valves!

As part of the annual service, the strainers on the TMV's are taken out and cleaned, so I don't think that will be the issue.

Can someone advise the fastest most cost effective way of identifying the TMV's that may have failed? Is it a case of removing each TMV and blowing down the valve to check the non-return is working and not 'letting-by'?

I am aware that a temperature could be taken off the hot water pipe when the pipes are running but haven't found this method totally reliable.

To give a full picture, the school also has no secondary return!

Any sound advice welcome.

Thanks

Max

 

[snowhead]

I used to maintain commercial buildings each with many, many TMV's
Crossover was a common problem where tank fed hot and mains cold were at the same TMV.

The best way I found to track down a faulty TMV,,

Gain access to the TMV and it's pipework at point of entry,
Place one hand on the Hot pipe as close as possible to the TMV,
Run the tap and the Hot pipe will warm up,
Close / let go of the tap and the Hot should stay Hot / warm,
If there is crossover the Hot will go Cold as soon as the tap is closed.

The future solution would be to fit Non return valves in the Hot at the time of the annual TMV filter clean.

 

[maxdani]

I used to maintain commercial buildings each with many, many TMV's
Crossover was a common problem where tank fed hot and mains cold were at the same TMV.

The best way I found to track down a faulty TMV,,

Gain access to the TMV and it's pipework at point of entry,
Place one hand on the Hot pipe as close as possible to the TMV,
Run the tap and the Hot pipe will warm up,
Close / let go of the tap and the Hot should stay Hot / warm,
If there is crossover the Hot will go Cold as soon as the tap is closed.

The future solution would be to fit Non return valves in the Hot at the time of the annual TMV filter clean.

There was a single tap causing the issue. We replaced the thermostatic cartridge inside the tap twice but the problem persisted. It was only when we changed the whole mixer tap that we fixed it. I don't quite understand how this could be the case as it looks like the tap just has two flexi's you connect to the pipework and nothing else that controls the temp or would cause the water to mix..

Anyway, thanks for your response.

Max