It does seem Part L was interpreted by people in different ways, I read on one council website how they felt having TRV in each room complied, and having programmable TRV heads clearly complies, and in the main the aim is for analogue control rather than digital (on/off) and the TRV lends itself to analogue control far better than a motorised valve.
How exactly does the thermostat not seem to be working well with the boiler?
A problem here, could involve the thermostat, the wiring, or a zone valve; making sure the system works as it should, would be a first step, before attempting to modify it.
This is very true, and with my own house it was a headache working out what went where, and what controlled what, and I had to carefully work out what wires went where, to be able to reuse the existing wiring to get the heating as I want it.
In the main the problem is, builder walk away without balancing the radiators, so on switch on, instead or a bit of heat going to all radiators, it goes to the easy path, until the TRV on that radiator starts to close, then next easiest path, and so on, so if any radiator is not warmed before the thermostat on the wall turns off the boiler, then it never gets warmed.
I read the instructions, it says fit a differential thermometer on each radiator in turn, and turn down the lock shield valve until different is around 15ºC the problem is I could not find my differential thermometer, so had to try something else.
My first step was starting as first radiator to heat up, to turn off the lock shield valve, wait for pipes to get cold, then turn back on ¼ turn at a time, until one pipe got warm, then move to the next.
It worked, but not A1, they still needed a bit of fine-tuning, by this time I had an electronic head for a radiator, which gave a display on the PC, so now I had
so I trimmed the lock shield so current never exceeded target, and except for room with bay window, where the sun was reason for over heating, all other rooms were spot on. The wall thermostat had been turned up full so sure the boiler did not turn off.
The next was the wall thermostat, unless using something like OpenTherm, we want the wall thermostat to only turn off on a warm day, so the temperature on the wall thermostat needs to be slightly higher than the TRV so it only turns off on warm days.
The easy way out is to get rid of wall thermostats, they are not required, as the TRV heads can tell the hub which in turn tells the boiler when to run, the EvoHome system you have a control panel on the wall,
but you can have a mixture, the Drayton Wiser system allows you to use both wall thermostats and TRV heads to control the heating, and it does have the option of three channels, two for heating and one for domestic hot water, the latter simply not used with a combi boiler.
EPH do a system where motorised valves and OpenTherm can be used, I think up to 10 motorised valves, one master thermostat and rest are slaves, but in the main better to only use the TRV heads, OK I have both, motorised valve turns off complete flat, which reminds me, we are due to have visitors, so need to go down and turn heating up.
