Radiators not Heating Up

plumb1_2

Ya that T with the 15 mm branch should be there, looking at the other 15mm coming up from the floor appears to be connected to the return. So it’s making a circuit and working by gravity.
But still doesn’t explain why the boiler runs when programmer off.
Think Vaillant boilers have a pre heat function ( summer/winter setting) but usually only on Combi 
Get the manual and turn the pre heat off, if it has it, then see what happens.

ThisIsWeird

plumb1_2 said:

Ya that T with the 15 mm branch should be there, looking at the other 15mm coming up from the floor appears to be connected to the return. So it’s making a circuit and working by gravity.
But still doesn’t explain why the boiler runs when programmer off.
Think Vaillant boilers have a pre heat function ( summer/winter setting) but usually only on Combi 
Get the manual and turn the pre heat off, if it has it, then see what happens.

The pump will be built in to the boiler, I guess? I'd assumed that the idea was that the towel rail would come on wherever either the CH or the DHW was also on, but it would be pumped around the TR? As you say, what makes the boiler come on now?