Sometimes, by accident you get something right. The old thermostat suffered from too much backlash and wildly fluctuating room temperatures. So, I bought an electronic version. It was difficult to find one as all the stock of Toolstation, Screwfix and Wickes was battery powered, a fact which is not always mentioned in the description. I do not believe in battery power for long term control systems. I prefer, fit and forget. Anyway I managed to find the Horstmann mains powered unit which had electronic control and TPI control software, which meant nothing to me. So, I purchased a unit from Amazon.
I fitted this unit and had an immediate panic, as to turn on the pump I had to go 3C past the known house temperature. So, I backed it down a bit and left it to it's own devices. Surprise surprise, the pump turned on sometime later and all was apparently well. The house temperature went up past the required point, so I backed the thermostat off a bit more. The result was the correct house temperature, except in the lounge, where the radiators had TRVs. I found out that because of the TPI function, the pump only runs for short periods, the result is that you have rapid indication of how the water is flowing in the system, by the radiator temperature. Hence it is possible to adjust the flow rates to improve the balance in the system. It also showed in my case that the lounge TRVs were set to too low a temperature to allow a TPI system to control properly.
In short I find that this product works extremely well .