Hot Water Control

[Davidgmitch]

I am fitting the ATF600 to my unvented system. The hot water is currently managed by the controller built into the boiler, which uses a tank thermistor to determine temperature and fire the boiler. A DHW pump is connected to boiler, no motorised valve is fitted for the water. The tank probe and CS92 are installed all ok.

I need to resolve how to turn the boiler on. There is no obvious connection on my Baxi WH46 boiler which could be used as a "demand for hot water". There seem to be three options;
1) interface Evohome to the QAA73 interface.
2) somehow connect a BDR91 in place of the boiler thermistor
3) Connect the pump to the BDR91 (at 230V) replace and Connect a second BDR91 to close the Roomstat connection on the bolier (demand)

Questions;
a)Is there a better way than (3) ?
b) Do I need to be concerned with any TPI type functions?
c) Should I remove the THemistor connected to the boile? (and presumably replace with a 10K resistor?)

Thanks in advance.

[Richard]

I am not quite sure to suggest, but the evohome system is an 'external' type control system and does not normally cater for when hot water control is done via the boiler.