Megaflo - temperature at tap is only hot when other cold taps on

[dilalio]

So... When the hot from the cylinder is isolated, you get nothing from the Hot side of "any" mixer on the system? Including all shower valves?

 

[dilalio]

Have you recharged the air bubble on the Megaflo?

 

[DP]

My cold taps are all fed from the mains cold

that is where the problem is

 

[chrisd1967]

Yep - air bubble is good, redid it yesterday just incase.

But... a breakthrough!

I did the test where I isolated the hot supply and went round each mixer tap and shower and confirmed that nothing came out on hot. All was good on all taps, but one shower still had cold water coming out when fully set to hot. After a lot of hunting and swearing in the loft I found an isolator, which happened to be the cold feed to that shower. Turned it off and hurrah! Boiling hot water out of every tap in the house now!

This does of course mean that I'm left with a shower that is only capable of putting out burning hot water, but I don't care because the problem has been found!

Thanks to all that helped.

The one thing I still don't really understand is why I didn't see cold water coming out of the *taps* when the hot is isolated, which had been fed back by the shower. The only place water still came out was that shower.

 

[dilalio]

Path of least resistance.
You have the culprit and it is a common one.

 

[jeff the gasman]

There has always been a bit of an issue with tepid water in the hot taps, which we have always just put down to water taking ages to arrive at the tap. Recently it appears to be worse, so perhaps the mains pressure has increased or something like that.

My only hesitation with the crossover theory is that when the hot is isolated, we don't get any water at all out of the hot tap. If it were crossover then you'd expect some cold to come out?

Yep - air bubble is good, redid it yesterday just incase.

But... a breakthrough!

I did the test where I isolated the hot supply and went round each mixer tap and shower and confirmed that nothing came out on hot. All was good on all taps, but one shower still had cold water coming out when fully set to hot. After a lot of hunting and swearing in the loft I found an isolator, which happened to be the cold feed to that shower. Turned it off and hurrah! Boiling hot water out of every tap in the house now!

This does of course mean that I'm left with a shower that is only capable of putting out burning hot water, but I don't care because the problem has been found!

Thanks to all that helped.

The one thing I still don't really understand is why I didn't see cold water coming out of the *taps* when the hot is isolated, which had been fed back by the shower. The only place water still came out was that shower.

Fit check valves to pipes and problem solved.
For now!

 

[chrisd1967]

Last question...!

I'll fit check valves into the cold and hot feeds of that shower. I assume I'll need to do both feeds as there's every chance the hot could feed back into the cold too.

Would a single check valve suffice, or shall I get a double?

Many thanks again!

 

[jeff the gasman]

Your call!

 

[dilalio]

And make sure you fit them the correct orientation.