Radiator Q: Partially-closed supply valve and open return valve same as vice versa?

ToTo_Man

Hi folks,

You may remember my posts around Christmas time detailing my mammoth task of balancing (and adjusting TRVs on) all the rads in our house in an attempt to reduce fuel bills. I'm pleased to report the my efforts seemed to have worked in terms of saving a few quid per week, although the downside has been an increase in sound affects from the CH system (clicks and clanks from the pipework, presumably due to me reducing the inflow and/or outflow to certain rads).

The rad/towel rail in the upstairs bathroom is one of the two rads in the house that don't have TRVs, just supply and return valves. To achieve a desirable temperature in the bathroom, since Christmas I've had this rad set so that the supply valve is partially closed and the return valve is fully open. This is one of the rooms that the clanking noises from the pipework is loudest in.

Last night a member of the family was taking a bath and set the supply valve fully open to maximise inflow to and therefore heat from the rad, and I noticed that the clanking pipework noises disappeared. But this setting makes the bathroom too warm for everyday use, so this morning I restored the valves to the previous positions, only this time I set the supply valve fully open and the return valve fully closed, i.e. the reverse of before. Since doing this I've noticed that the clanking from the pipes hasn't been as noisy.

I was therefore wondering what the mechanical difference is between a partially-closed supply valve and fully-open return valve, and a fully-open supply valve and partially-closed return valve? Is there any difference between these pairings in terms of the strain it places on the boiler and its pump?

Thanks in advance...

bordercars

im sure some plumbers will reply, but arent the non trv rads shunts, so that if you boiler thermostat goes wrong the non trv rads can take all the heat. what effect this has on the flow rates im unsure