It is very good. There are of course many central heating systems but I have it seemed been plagued by two common faults.
1) Micro switches in motorised valves. With the older systems the thermostat does directly control the boiler but instead opens the motorised valve. This in turn starts the central heating boiler. Sometimes manually latching the valve as one would do to bleed will get central heating running again but this means the radiators will heat up in Summer so only temp fix.
2) Balancing radiators. In the old days as stated on the article out of balance radiators would mean some don't get hot. But with the newer systems the thermostatic radiator valves will close the supply to radiators in warm rooms so diverting the supply to cold rooms so even with all the lock shield valves wide open the system will in the end heat all radiators.
However unlike the old boilers which only monitored the temperature of the water leaving the boiler the new boilers also monitor the temperature of the water entering the boiler in order to keep it cool enough for condensing to take place. The boiler does not simply switch off and on but varies the flame height so supplying just enough heat.
While running this works fine. As each radiator becomes cool the thermostatic valve opens allowing hot water into it and soon after it becomes hot the valve will close again controlling each room independently.
The problem is when the system has been turned off. If the lock shield valves are wide open as the system starts it pushes all the water through the easy radiators. These quickly get hot and hot water is then returned to the boiler which in turn turns down the flame height. So until those first rooms have got warm the other rooms are not heated. In fact open doors can mean the other radiators never turn on. I have come across this with many houses. And since in the end the radiators do get hot it just takes a long time the occupant can be unaware there is such a simple to cure fault. They just think the boiler is not big enough.
There also seems a lack of up-dating with many plumbers and they still do things like leaving one radiator without a thermostatic valve.
Theory is on a hot day all valves are closed so when boiler starts the by-pass valve opens straight away sending hot water back to the boiler. With good boilers the software if the boiler runs for under a set amount of seconds extends the time before next run. Conversely if under set amount of seconds it will shorten the time before next run. So during the summer it will likely only start up 6 times a day which is wanted anyway to stop the pump from sticking.
But if too much water can go around the system then the boiler thinks it's colder than it is as the return time is exceeded. A small towel radiator likely will not allow enough flow to fox the system but a radiator in a hall etc will.
But because for years it was standard practice for the radiator where the electric thermostat is placed not to have a radiator thermostat it is still done today.
The whole idea of an electric thermostat is to stop cycling in the summer so should not be in coolest room any more but in the morning sun. So stopping the system from running when we are likely to have a warm day.
However unlike the radiator thermostat the electric one can also have a timer built in. On the old system this means you can set 4 different temperatures at different times of the day. On a new system when set to a high temperature it will never switch off and the radiator valves will do the controlling but when set to a lower temperature the house reverts to old pre-radiator thermostatic valve days and each room is controlled by the setting of the lock shield valve.
Although careful selecting of radiator sizes and trimming of the lock shield valve can work. In the main it doesn't and you get warm and cold rooms while set to low temperature. As one would expect one can get some real odd results which will also change according to wind direction and outside temperature.
Good central heating engineers can combine the two systems to very good effect. But a bad heating engineer can leave a house with a completely uncontrollable system. In the main to be fair it's the DIY man adding electric thermostats to a system designed not to have them.
As an electrician I get called to change a faulty electric thermostat realise what's wrong but lack the equipment to be able to adjust the system even if the house holder will pay for our time.
I have a digital thermostat with two inputs and can measure the differential between in and out pipes on a radiator. In the past I have tried to set-up a system. If starting from cold not too hard. But once house has warmed up the switching of all the radiators in the house can produce some very varied results. However get the heating engineer who is doing it every day and he works more from instinct than meters and can do in half an hour what it will take me half a day to do. I may do it 4 times a year he does it at least once a week and now I don't even attempt to set them. I give the house holder his number and accept he has a skill I lack.
So what I am saying even if you have read and understood all I have said. You can expect to spend two days tweaking the lock shield valves and even then wind direction and outside temperature can upset it all. If they will not call the guy then all I do is close a valve down on a radiator near the boiler and then slowly re-open 1/4 turn at a time until I feel hot water flow counting the turns. Then set rest to same amount. Not the right way but works most of the time and does not take too long.
