Strange Fitting?

What is this?, its installed between the mains and a electric shower, when the weather gets very hot the (newish) shower stops flowing, its a dedicated flow to the shower.

Looks like a (fairly old) double-check non-return valve to me. I can't see the part number from the photo but Westco are still in business, try asking them.

I speculate that the inlet temperature is getting too high, say 30°C but check the shower spec, on hot days day so the shower is cutting out. Would probably be okay if you could run the few litres of tepid standing water through before turning the shower heater on. Is the shower on the end of a long branch or would running a bath/basin tap or flushing a toilet be a possible method of flushing the warm water out?

Thanks Chuck, thought it might be something like that and just wondering when the water heats up if the clacks/flaps are hydraulically locked in although one would think that the solenoid valve should still open releasing the pressure, assuming the mains flow is up and under the solenoid valve seat, best advice is probably to remove it.

Or maybe just a mini manifold with a male & female connection.

It’s either one or the other eg Verifiable via the ports or a temperature tempering valve eg slows or increase the flow depending on incoming temp fancy flow regulator

Might have a filter as well as check valve.