I've got ebusd reading the flow and return temperatures from the boiler (red and Green) (Vaillant EcoTec Plus 637) and some thermocouples on the pipes about 1.5m away from the boiler (yellow and blue). The flow as reported by the boiler is matching the thermocouple both when the boiler is off and on (accepting that the boiler EBUS readings are 2.5 mins apart so misses some of the peaks).
However the return tracks when the boiler has been off for a while but then is ~10degrees hotter than the return 2m from the boiler when the boiler switches on. Our system has both the internal boiler bypass and an external one about 0.5m away from the boiler and I assume this is to caused by them but I can't understand why it is happening when the boiler has started from cold as all TRVs should be open.
Any ideas?
However the return tracks when the boiler has been off for a while but then is ~10degrees hotter than the return 2m from the boiler when the boiler switches on. Our system has both the internal boiler bypass and an external one about 0.5m away from the boiler and I assume this is to caused by them but I can't understand why it is happening when the boiler has started from cold as all TRVs should be open.
Any ideas?