HW Feeder tank gets hot and overflows

[birchjc]

Advice Please!
Hot water is coming up the pipe that would normally provide cold water to the hot water tank, it fills the HW Feeder tank and causes it to overflow. The vent is dry and the ballcock is working. The Feeder tank is warming up and I an feel the pipe at the bottom is hot - pretty sure this is the CW feeder to the HW cylinder.
So the HW cylinder must be pressurised to mains pressure (central heating feeder tank is lower than the HW feeder tank). 2 possible causes in my mind;
(1) HW cylindar coil has a leak letting mains pressure in - but Central heating is from a lower feeder tank so I don't understand how that could happen.
(2) something in the HW/CW system is leaking mains pressure through e.g. mixer tap or perhaps the shower pump I fitted 2 months ago that has started "juddering" a few days before this HW tank overflow incident.

My best guess is #2 and that it is linked to the "juddering" of the shower pump. I suspect the juddering is some form of "turn the pump motor on" sensor or non-return valve. I switched off the power to the shower pump when it is not being used... my wife first saw the problem when having a shower...

Can you suggest how to test this theory or tell me if my logic is wrong and there is a possible other problem (I fitted other mixer taps when I put the shower in 2 months ago, but the problem is only just occurring now). I did cheat when fitting the shower pump and used a mains pipe rather than pipe right the way back to the HW feeder tank (feel guilty now for the short cut! Suspect this is retribution!)

Thanks

 

[Resolute]

The feeds to your shower pump must be balanced, as you've used mains cold this won't be the case. I suggest that you re-do the cold feed to your shower pump from your CWSC - hopefully that will solve the problem.

 

[Gray0689]

All you have done is basically looped the mains to the hot vie the pump for one you should not have mains on a pump and you have probably wrecked the pump too
As said the shower needs dedicated feeds from cylinder and tank to give you a balanced system get a decent plumber in to sort it as I guess you have wasted more money than it would of cost in first place

 

[diamondgas]

:iagree: with resolute --- spot on I'd say 🙂

 

[birchjc]

Thanks all.... I realise my mistake! I am now plumbing the cold water feed back to the feeder tank. Any idea why it all worked fine for a month or so then failed? Is there a non-return valve on the outlet of the pump that has now jammed open? (Pump Details: Turner Stuart Showermate Standard 2.6 bar twin).

 

[Gray0689]

Probably and you probably have ruined it

 

[Gray0689]

Ps its also illegal to pump mains water

 

[diamondgas]

lol ... To find out for definite it's the pump cap off the cold to it and see if the tank stops overflowing ... You still need to re-pipe it correctly though 🙂

 

[PlumbBobBob]

agree with everyone above needs redoing urgently imho