doozer wrote:


As you can see the Honeywell timer box has been bodged to the wall;

There are, I think, screws underneath the Honeywell box. Loosening
these will allow the controller to swivelled forward away from the
backplate; pull the plug first since live terminals will be exposed.
You don't have to remove the screws. They are often lost by those who
do remove them, which may be why it's wobbly.

using a standard electrical box.

Probably only one fixing screw will be holding it.

(I believe unvented is the technical term)

It is. Get the installation & maintenance manual from the
Heatrae-Sadia website.

I do not think that the discharge pipes from the two safety valves
(Expansion relief [downstream of the pressure reducing valve] and the
Temperature & Pressure relief [in the cylinder]) have been done
correctly.

There should be a tundish (it could be behind the cardboard label).
There is a 15mm branch below the cardboard label going to the left; I
suspect this is the boiler safety valve discharge. It should have a
separate pipe.

Either one of the two safety valves on the unvented cylinder should be
able to discharge full-bore without causing a flood. You also need to
see is either of them is dripping or discharging, since this indicates
a fault that needs fixing.