Is protection required for the pump?

[ericmark]

I have had a plumber look at my system, and he tells me the domestic hot water should be left as uncontrolled thermo syphon as there is no by-pass valve or run on with the boiler, and so having uncontrolled (other than time) DHW means there is some where for boilers heat to go when closing down. OK I accept that, makes some sense, and ½ hour per day DWH in summer does keep DHW hot.

However the central heating is worked by two pumps, one for main house, and one for flat under main house, both have TRV's on every radiator, there is a radiator in the bathroom without a TRV but it is on the thermo syphon not pumped supply, the wall thermostat in main house is linked to 4 of the TRV heads so they should work together, however there is a chance that all TRV will close and the pump is still running and since pump on return it could could cavitation, not sure if this would damage the pump? and not sure if a by-pass valve will work on a pump connected to the return?

Do I need to do anything? If so want to discuss with plumber before Monday as he is due to fit motorised valves so radiators don't thermo syphon so coolant will be dropped, so new water and inhibitor mix will go into the system, so any changes I want doing before new inhibitor added.