Header overflow - should be so simple.

[Terry Godber]

SOLVED!
A ballofix 1st installed to allow isolation of a gravity feed, then years later connected in reverse to mains pressure to avoid a capped tail and allow use of mains or gravity was caused to fail under the mains pressure leading to a mains water backfeed via the ballofix to the header tank.
Big thanks to all contributors especially Ian10261 who asked the question leading me to check out the failed component.

 

[Ric2013]

Help me get my head around this, please. So the mains supply pressure was pushing water backwards through the Ballofix and into the low pressure cold pipe?
Can you explain how this was able to backfeed the cistern via the one-way valves? Are we correct that the one-way valves are letting by in reverse direction?

 

[rpm]

This just gets stranger and stranger!
Isolating valves and non return valves not working.

 

[Ric2013]

This just gets stranger and stranger!
Isolating valves and non return valves not working.

I've already explained, as have others in this thread, why that could be in this specific instance.

 

[rpm]

I've already explained, as have others in this thread, why that could be in this specific instance.

All I said was it was a strange situation so why you jumping down my throat.

 

[Ric2013]

That wasn't how I meant you to feel, so apologies if that's how I've come across.
All I meant was that that I thought your comment suggested that you'd only just seen the bit about the one-way valves not being one way and the isolator not isolating and hence the thread was becoming 'stranger and stranger' and I wondered if you'd read the thread in its entirity.

 

[rpm]

I've followed it from the start, perhaps not fully understanding it all but none the less puzzled considering all the valves in place and their functions. Well aware of strong and weak non return valves I might add.