Fitting Thermostatic Rad Valves

[dbharrison]

I am intending to fit Thermostatic Rad valves to all my radiators. I have heard that it is important to leave one radiator without a TRV but do not really understand why this is necessary. Also my current system does not have TRV's and uses a single room thermostat mounted in the hall. When TRV's are fitted, the pump will run when the hall temperature is below the setting of the room thermostat but if the hall TRV is on a low setting the pump will run continuously, as the hall radiator will be off.
What is the correct way to resolve this?

you don't fit trvs in the same room as a room stat, they play against each other.
when one rad is left without a trv that rad is used as a bypass. in your case the hall rad.

most boilers have a bypass fitted to them now days. and if yours is an old system boiler does it have a pump over run ?
and is it a y plan or s plan

[fuzzy]

you shouldnt use a rad as a bypass, you must hve a regulating auto by-pass. doddle to fit, just link between flow and return

it's not a regulation you must fit a auto by pass, it is still acceptable to use a gate valve as a bypass by many boiler manufactors.
and im talking when systems where back boilers and gravity long before auto bypass were being fitted. and as many still have gate valves fitted, and theres no regulation to state they must be changed.

[fuzzy]

it is contained in the best practice guide for domestic heating installations. its all to do with energy efficiency. if you are sending heating water round a rad when that romm does not request heating it is a waste. if you use a gate valve(usaually a lock shield in my experience!) then in high demand the boiler is heating water then wasting it round a small loop therefore an auto by-pass will be closed in such cases and not waste water.
boiler manufacturers are interested in making the system and boiler safe and therefore any by pass will do for them