When checking that I had properly closed the integral fill loop tap, I found the bypass pipe was hot. (
The pipe runs along the front of the boiler just above its open bottom and is touchable when topping up the system pressure using the integral filling loop tap). I checked the filling loop tap because the system pressure had unexpectedly risen after topping it up and I thought I hadn’t closed the tap properly but it was closed.
I didn’t expect the bypass pipe to be hot because the heating had not been on very long and was not up to temperature. The TRV’s should not have been closed or closing. Plus, the hall radiator has its TRV head removed and the bathroom radiator is the heat leak with no TRV.
Wondering if a permanently open bypass could thwart my attempts to balance the system and get a condensing return temperature (less than 55’C), I checked the pipe’s temperature during several cycles of the system heating up and cooling down; and found it followed that of the flow pipe. I rechecked it with all TRV heads removed with the same result and also with all lock-shields fully open.
The radiators are: ( using
Panel Radiator Output Calculator | Castrads)
· Bed 2 - 1040 watt older single panel with TRV
· Hall - 1720 watt older double panel with TRV head removed
· Bed 1 - 3097 watt older double panel with TRV
· Lounge - 3441 watt older double panel with TRV
· Bathroom - 260 watt newer single convector with no TRV
· Kitchen - __
736 watt newer single convector with TRV
10294 watts total
The house is a bungalow of approx. 66 sq. metres. The boiler has a fixed speed pump and max output of 24.7kW in CH mode, modulating down to 5 or 6 kW. I’ve been advised that the output of the boiler may be too high for the heating load and the fixed speed pump circulates the water to fast for good heat transfer from the radiators, hence, the high return temperatures; which presumably is exacerbated if the bypass is stuck open.
Even with the boiler set to 60/65’C, the return temerature from the radiators rises very quickly to within 3 or 4’C of the flow with all radiators getting hot and without any cold spots. It's the same with all TRV heads removed (
the valve pins move freely up and down).
The TRV for the hall, where the wall thermostat is located, is removed to stop the two fighting each other.
The system was flushed for 3 weeks back in the summer and each rad gets hot quite quickly, so I'm hoping the pipework is not sludged up.
Pipework is 22mm from boiler to branches then 15mm to radiators, except Bed2 and Bathroom which are on the same common 15mm branch and are the slowest to heat up.