Radiator Feed Before Zone Valve ?

molerat

My son has just moved into a house. We put the boiler on to get hot water and noticed the uncontrolled rad in the hallway getting hot. I thought maybe the zone valve was stuck but no other rads were on so went and had a play and noticed a tee between the pump and zone valve with microbore running off, I assume, to the radiator on the other side of the wall. The previous owner said she hardly needed the heating on - not surprising as the hallway rad is on all the time HW is selected. The question is - is this normal and if so why ? Open vented system all on microbore BTW.

Ainsley1

Many modern boilers require pump overrun I.e. the pump to continue to circulate water after demand ceases for a few minutes to cool the boiler heat exchanger. For this to work there needs to be a path to circulate. Perhaps that radiator is part of that path?
Not a fan of that method for the reason you located -heat output when not required. Better solution is to have 3port diverter valves connected such that there is a secondary circuit for circulation when neither heat or hot water is demanded. This can be through the radiator circuit through an uncontrolled radiator that is always 'open', typically bathroom as the very small bit of extra heat is not really an issue for the short overrun time (5 minutes typically) but you are ensured that boiler overrun works well.

Might not be like that on your system though

Crinkmeister

I agree with Ainsley1. It's a bypass.

molerat

Been on line looking at installation instructions for the boiler and it seems the only feasible / simplest way to stop this rad heating up needlessly is to convert to a Y plan system as it states a bypass is not needed as it automatically diverts to HW when there is no demand. It may lead to a longer over run though as it is a simple 80 deg switch dissipating into hot water rather than cool air but will be on a longer piped run using 22mm. Now need to check if there is 3 core going to the tank stat. (although it may be fairly easy to run as the tank is almost directly above the wiring centre on stud walling)