We have an old indirect heating system fired by a gas back boiler. When fired up to heat water only, hot water is flowing into the smaller of the two header tanks via the overhead expansion pipe causing the tank to overflow.
Is this due to a split inner cylinder or calorifier in the indirect cylinder.

Paul, June 2008

follow your cold feed to where it joins the heating pipework in airing cupboard thats the most common place for a blockage.


try turning the pump speed down to min.

also you can find a drain cock on a rad, secure your ball valve.
and drain the system if the system drains and tank still full you have located your blockage.

hi-spec plumbing & heating, June 2008

Thanks Hi -Spec.
Tried your test and water still keeps flowing into small header tank. Dont understand where blockage to cold feed could be and why any water would run if no new water was entering system?

Paul, June 2008

no sounds like a blockage in the cold feed.

shut the gate in the airing cupboard that feeds the cylinder from the large cws tank in loft.
does it stop. the water coming out of the vent pipe ?
if not you have a blockage.

hi-spec plumbing & heating, June 2008