Help! Builder has messed up central heating

[I am bonkers]

There must be a bypass pipe connecting the input to the output of each rad. The three-way valve then determines how much flows through the rad and how much flows down the bypass.

Why not just use one of the existing rad valves it does not really matter which. it will facilitate balancing or shutting off the rad. so long as you fit the by pass pipe.

If you fit a by-pass, the natural flow will be for most of the water to go via the bypass; this because the resistance is less in the bypass. There needs to be a way of restricting the flow through the by-pass so the rad receives the required flow. This can done either by fitting a flow restrictor in the bypass or by using a three way valve.

Can't believe you're even debating this. If you're going to the bother of fitting a surface mounted bypass why not just duplicate the original 2 pipes in the lounge? Guaranteed to work. Nothing to adjust, maintain or fail.

 

[tropical lounge]

Unfortunately, because of the room layout, re-running surface mounted pipes isn't practical. The lounge door is in the centre of the wall and there's a radiator on either side so it would mean digging up the flooring to get the pipes from one side of the room to the other, unless the pipes went up and over the doorway (can't go the other way because of fireplace) . Similarly in the kitchen, there is now a run of newly fitted kitchen units to get past between where the pipes would enter and the radiator. A bypass pipe, if it would work, would at least be just under the radiators themselves and could potentially even be hidden behind skirting.

 

[I am bonkers]

Unfortunately, because of the room layout, re-running surface mounted pipes isn't practical. The lounge door is in the centre of the wall and there's (now?) a radiator on either side so it would mean digging up the flooring to get the pipes from one side of the room to the other

 

[tropical lounge]

There always was a rad on either side of the door. Before the work was done, the surface mounted pipes in the lounge went underground briefly just to cross the door threshold. All this old pipe work was removed when the floor was dug up and re-screeded.

Since there doesn't seem to be anyone saying that the 3 way valve and bypass definately won't work, I'm leaning towards trying this on one radiator in the lounge initially to see if it works. Not ideal and the builder will be taken to task over it - talking to the electrician recently, was told he knew someone else the builder had done this to (may try and get their name)!

It may be while before I can get it done, but will let you know the result.
Thanks for all your input, very much appreciated. Off to put hat and gloves on and start cooking dinner.....