by ericmark »
Thu Oct 17, 2019 6:31 pm
N/C means normally closed and N/O means normally open however what is normal can change, so although N/O would be used in most thermostats to power the central heating, with the flowmasta thermostat I fitted there was a small switch so N/C could be used. The idea was N/O could be used to supply an air conditioning unit, so if the batteries become discharged it would not auto start, but it did mean you could use N/C to supply central heating.
In the main we have the programmer that supplies the thermostats, and the thermostats supply the motorised valves, and the motorised valves supply the boiler, however in some cases the tank thermostat supplies the boiler direct without going through the motorised valve.
With some of the Smart thermostats the thermostat supplies the programmer and programmer does switching.
In the main we use plans, there is the Y, S, W and C the latter came in at least three versions, a combi boiler will normally use a W plan inside the boiler, but for us the user it just has a thermostat there is not programmer.
There are three basic connections for the thermostat, one is 230 volt, the other is 24 volt and last is a varying voltage that does not switch boiler off/on but tells the boiler what output to deliver.
So step one is work out how your boiler is controlled, with Com and N/O marked it is unlikely to be connected to the eBus, but could be either 24 or 230 volt.
So what type of boiler? are there motorised valves? if so how many ports? is there a programmer? As said normally Com to N/O would work, and on odd time Com to N/C with some rare systems both N/O and N/C both used but rare.
