So is this your home shower? How come you do not know if the cold is
pumped?
Id suggest either the pump is stuck or not working. Its probably time to
track the route of the cold feed and see what you find.
Brian

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On 14/01/2019 22:30, asalcedo wrote:
After several months away I find that there is no cold water in my
shower.

The hot water is fine.

The shower has a thermostatic mixer. When I open the water, only hot
water comes out.

The shower is fed with a Stuart Turner Monsoon pump. Which, in turn, is
fed via 22 mm copper pipes from the tanks in the loft.

The pump works fine with the hot water. With the cold water, since there
is none, it does not pump any.

I seems like an air lock. Thus, I have removed the mixer and fed the
cold water pipe on the wall with water with mains pressure (about 2.5
bar) via a garden hose connected to a tap nearby.

After several minutes, there is still no cold water flowing.

All the valves of the cold water pipes are open (as they were before).

Is there a non-return valve in the pump?

What else can I do to fix this?

Where does the cold feed come from? Does it come from a tank, and is it
pumped like the hot?