DIY Doctor

Wiring advice for swapping Honeywell BDR91 for Heatmiser RF

Postby Bluecollie » Thu Sep 17, 2020 12:08 pm

Hi, I have a Warmflow combi boiler, with a Honeywell BDR91 that I'm replacing with a heatmiser rf. The Honeywell is wired L&N which is obvious and Black to A, Grey to B. On the heatmiser am I correct to put Black to Com1 & Grey to No1. Using heating only not hot water. Thanks
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Postby ericmark » Sun Sep 20, 2020 6:42 am

The Heatmiser RF does not give a lot of info, it would seem there are three sets of contacts, two for the motorised valves and one for the boiler, and it seems you only need to use the set for boiler and the live supply to power it.

I suspect there is a delay and the valves are opened before the boiler turns on with a S Plan installation, but there does not seem to be much about the unit.

The Honeywell BDR91 is a very good quality unit, it has a fail safe system, if it looses the RF link it closes down, (i.e. dead batteries in thermostat) where some of the cheaper units can keep boiler running, it also has built in anti-hysteresis which with modern gas boilers was not really a good feature, but with oil it worked well, it seemed a simple thermostat, but in fact the BDR91 was a very good unit.

I made a mistake, easy to say in hind sight, I swapped the Honeywell for a Horstmann programmable with the idea it would turn up/down the temperatures rather than turn off at night, theory was good, build quality however was not, and if it lost the RF link, the boiler would continue to run.

I look at the price of the Heatmiser RF and it seems to do so much more and is so cheap, just like my Horstmann, I would make sure you keep the old unit.

I like the idea of the Heatmiser RF and if it works well would consider fitting one in the flat under my house, as rarely used, and would be handy to be able to switch it on remotely when we get visitors, but I do question why my wall thermostat allows me to alter temperature remotely, all I really need is to turn it on/off.

I do wonder if my thermostat really needs all the controls? I know mine has geofencing connected to our phones, and also occupancy detection should our phone not be home but we are, and uses algorithms or some thing to work out when it needs to start heating to be warm on our return, my Nest Gen 3 is very clever, but as to if I really need it to be so clever, not so sure, and with all that, it still does not connect to the Energenie TRV heads, which independently can use geofencing to control heating.

The problem is we know they work, but we don't know if they work in an efficient manor?
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