Indirect coil leaking again?

[Dripping]

Hi,
Don't know whether to post here on on plumbing as the two are conjoined.

Solid fuel backboiler - 28mm pipes gravity fed to/from indirect coil which also has immersion element for summer use. and 1 heat sink rad. open Expansion tank -

joined to pumped CH rad system 10 rads upstairs and down.

When gravity return reaches heat, pump switches on and diverts hot water round other rads.

Backboiler needs replacing, turned off expansion stopcock, drained system, removed boiler...central heating keeps refilling.

Expansion tank is bone dry.

So... I take it the coil has gone in the cylinder again.

This cylinder is only 7 years old. The previous indirect coil bust as well after less than 10 years usage.

Can I confirm this in any way or have I already done so?

Seems a short lifespan for the coils, any reasons these are prematurely failing? Water supply is high in iron (borehole) and acid. (corrosion, electrolysis?)

Can I cap the coil ends and still safely use the electric immersion for now?

 

[dontknowitall]

Was any inhibitor put into the system after the last hot water cylinder change?

 

[Dripping]

Hi,
thanks for reply,
Yes, the system has been drained, flushed and refilled will clean water and fernox inhibitor approx 3 times since cylinder was fitted. This was due to rad replacements during ongoing renovations.

Fernox was used because it seemed prudent to do so giving the high levels of iron in the water (50 times recommended levels for potable water)