I have today flushed out my central heating system with Fernox restorer ready to add Inibitor,whilst bleeding out the air I noticed that some of the radiator valves are in the flow and some are in the return.Is this normal ? or should they all be in the flow pipeline.
Both! Every radiator should have *two* valves - one on the flow side and one on the return side. One should either be a TRV, or an adjustable manual valve with a knob to turn. The other should be a lockshield valve - similar to a manually adjustable valve, but with a cover instead of a knob. This type can only be adjusted with a spanner - which is necessary to do when balancing the system.
It doesn't really matter which valve is on the flow and which on the return - except that *some* TRVs are designed for the flow to go in a particular direction - and so have to be on the appropriate side.
It doesn't really matter too much, Anna, with one exception. Some TRVs are unidirectional - meaning they must be fitted to allow the flow to go a specific way. Sometimes they are mechanically reversible, in which case they can go at which end you like as long as the flow direction through the valve is correct. There is normally an arrow indicating flow direction.
Nowadays, though, most valves are bidirectional and it doesn't matter what you do. These usually have an arrow with two heads stamped on the valve body.
If the orientation is wrong on a unidirectional valve, a typical symptom is a vibrating or rattling noise from the valve, especially when nearly closed.
Most modern TRVs can be in either flow or return. Indeed, there is a good reason to favour the return, as the water temperature can be up to 10 degrees lower, providing less parasitic effect on the TRV's room temperature sensor.
Christian.
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