Airlock ? No hot water to pumped shower

Since a couple of weeks I notice that the shower is not as hot any longer as it was. I blamed it on not enough hot water in the tank and used the immersion. No difference, now I adjusted the thermostat in the shower tap , no differenec. Actually after a couple of minutes just get very luke warm water. The sink in the bathroom gives very hot water.

When looking in the hot press I noticed that the hot water pipe to the pump ( only used for the shower) was not really hot , neither the pipe from the pump to the shower. The pipe from the tank to the tap was really hot. So my best guess ( and cheapest) is an airlock somewhere between the tank and the pump ? Or is it more likely that the pump is gone ? Pressure is still perfect in the shower.

Don't know about yours but we had a problem with ours immediately after installation - intermittently there would be no water. The plumber came back several times and adjusted the pipes in the hot press to no avail.
My daughter finally discovered that if no water was forthcomong then hold down the handheld showerhead and hey presto there is water.
Your problem is probably different but HTH somebody.

It could be a blocked gauze filter at the pump (on the inlet side) or the thermostatic cartridge in the shower valve could be faulty.