mains cold water causes hot water cylinder to vent any ideas

[Popejp]

Abt 10 days ago installed a shower pump for new garage extension which is now an en -suite bedroom and since that wheather thats caused the problem i doubt it, whats happening is when i turn on water mains from downstair toilet to bring cold water into the house somehow the hotwater cylinder is filling up and forcing itself out of the hotwater vent into the cold water storage tank into attic causing water to pour into my conservatory which is annoying, plumber says its split pipe in hot water cylinder so had that replaced and still same problem, he changed motor valve same problem turned motor pump for radiators down and temperature and still no luck even had a new electronic stat anyone out there know what my problem is coz i've had enough chuckuing money down the drain pls any good advice will be great, my system is an indirect system

many thanks

John

[plumbbob]

I am disappointed the plumber thought the problem lay with the cylinder as not symptom you describe points to this fault.

Need further info to help.

Explain exactly how is the shower and pump are connected to the system?
What sort of taps does the new basin have, two taps or a single mixer?

[wimiu012uk]

Sounds like somehow you have connected mains cold water to hot water system which is then forcing water into hot water tank under mains pressure rather than under gravity feed from cold water header tank. I know plumber has said split pipe in hot water tank and you have replaced it. Replaced what ? as split pipe would be an integral part of hot water cylinder so complete tank would need to be replaced and then you would be able to check if it was a slit pipe in cylinder by putting water into pipe via a hose pipe.
I sugest rechecking where pipes have been plumbed into and if they have been plumbed into hot water system by mistake you would also get a much better flow out of hot water taps as they would be under mains pressure.
Hope this helps.

[stoneyboy]

Popejp,
If you are saying that when you turn on the mains into your home the cold water tank feeding the hot water cylinder overflows then you should be looking at fittings where you have both mains cold and tank fed hot water. This may be a shower valve or kitchen tap. If you have not replaced the hot water cylinder the coil in this may have perforated.
To help you we need more information.

[TheDoctor5]

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