No hot water. 3 ladies in the house. I'm feeling the heat (but not from the water)

[Mike Jones Amber Hill]

Here's the problem:

• Central heating (wet underfloor) is fine.
• Hot water comes out of any tap/shower for 60 seconds, then cold.
• This happened suddenly, was working fine before that.
• Boiler working OK.
• Pipes within a couple of metres of unvented cylinder are hot.
• Pressure gauge to cylinder is broken (so can't read input pressure)
• Supplied by water main, good pressure in house generally.

My Theory:

• Water is hot in the cylinder and therefore heats up water in the pipes gradually.
• Whet tap turned, hot water in pipe comes through. This quickly runs off and only cold water follows.
• So, the hot water in the tank is not being pushed through the pipes, it just stays in the tank.

Is that a good theory? And if so, what would cause this? Tried turning of mains input to cylinder, opened hot tsp til it stopped, twisted the tun dish for a bit, refilled and the closed the hot tap. Didn't fix it. I am thinking do I need to drain the cylinder completely via the drain valve at the bottom, then refill? Also, could it be the silver automatic valve causing the problem? I actually have two cylinders side by side so hard to see how both ports would fail at the same time?

Any help? The ladies will be home soon 🙁

 

[Mike Jones Amber Hill]

If the mixer (tap or shower) is off, how can they back feed? Are the hot and cold connected before they meet the mixer valve I.e mixer valve closed - doesn't that close both flows!

 

[ShaunCorbs]

If the mixer (tap or shower) is off, how can they back feed? Are the hot and cold connected before they meet the mixer valve I.e mixer valve closed - doesn't that close both flows!

Exactly that's why normally you only have one lever to turn on the other is temp

 

[Mike Jones Amber Hill]

So when the Lever is closed it can back fill because the hot and cold meet and mix before the lever closing.

In effect they are then in one pipe, and the one with the stronger pressure can push the other back down the pipe, or hold it at bay, stopping the hot having any flow to outlets.

This should not happen because a NRV acts as a barrier to stop back flow. If an NRV has failed it would allow the ba flow and this could be our problem?

We would need to isolate each mixer, and then turn on, one by one, to see when the problem returns.

Is that right?

It couldn't be an airlock in the pipes instead could it?

 

[ShaunCorbs]

Correct the nrv stops the back flow

Can happen depending on your mains water pressure eg higher than your hot

No you wouldn't get any water then

 

[Mike Jones Amber Hill]

Last question, any idea ballpark what it will cost to fix. I imagine it's a pain of a job as its a process of elimination and also access to isolation valves might be an issue

 

[ShaunCorbs]

Can't say due to it being a pain if the pipes are boxed in etc

You could do most of the donkey work eg finding the pipes making access etc

 

[Mike Jones Amber Hill]

Thanks for your advice, time to get someone in,

 

[Ben-gee]

If one of the bath mixers is playing up, I’d start there first.
Amazing how a thousand pound fancy tap can be brought to its knees by a 10p plastic nrv.