I have a Worcester Bosch Greenstar 32Cd combi boiler connected to a number of rads with Danfoss ZWave valves. The valves are controlled from HA, but the boiler is controlled from its own Digistat RF.
Basically, the Digistat is programmed to whack the temp up to 25C whenever we are likely to be wanting heat, and the rad valves are programmed for the actual temps we want. This has worked OK-ish, but now the controller for the Digistat is on its last legs, with multiple LED segments failed, so I’m exploring options.
Ideally, I’d like to ditch the Digistat completely and control the heating side of the boiler from HA. I’m happy to leave the hot water side as I never change the programming on that unless we are away.
I’ve explored putting an HA-controlled switch into the existing control circuit. The approach being to switch off the Digistat and overide it using a switch connected to the Frost Stat interface on the boiler. However, this didn’t seem to function as expected. I assume this is a consequence of having the DT10RF (the boiler end of the Digistat) attached the boiler.
I can’t simply remove the Digistat and associated DT10RF (the bit at the boiler end) because the DT10RF also controls the hot water programming.
Has anybody else been down this path recently (last thread I could find was 2016)?
It all depends on how the ‘thermostat’ is connected to the boiler.
In my case there were literally two wires coming from the boiler to the thermostat unit, and when the thermostat was under the prescribed temperature the switch inside it would close, connecting the wires together thus starting the heating loop in the boiler. Effectively if I had removed the thermostat and simply connected the wires together the heating would be on permanently.
So all I did was remove the thermostat and replace it with a relay that is activated by a NodeMCU (which is flashed with esphome and controlled by homeassistant). Homeassistant now simply toggles the relay based on my pre-programmed rules around temperature and occupancy, which is derived from other sensors connected to it.
Thanks, but it’s not that simple. The Digistat is connected over RF to the DT10RF.
I have considered hacking the RF protocol and emulating it using a simple RF transmitter. ISTR somebody else may have done that on another forum, but I’m exploring other approaches.
You’re saying that the digistat connects with the dt10, which then connects to the boiler? So the question is how does the dt10 connect to the boiler to tell it when the heating should be on or off?
It is that connection that you need to ‘hijack’ to exert control.
In that case you maybe stuck with sending it an rf signal as you described, unfortunately. Unless you can economically replace the dt10 with something more ‘tinkerable’.
There are different hookups allowed.
I assume you are in the UK ?
UK heating installation technicians are not allowed to install just the switch on / switch off stuff any more.
So there is the remote thermostat (nearly as bad as on / offf apparently) and then there are smart thermostats (currently highly favoured, like nest et al and expensive and not very flexible)
You have tremostatically controlled radiators so you don’t want the ‘smart’ options, your smarts are elsewhere.
Ditch the DT10, get the remote thermostat face panel replacement (the other end of the DT10) Then there is a loop for the thermostat (consult the wiring diagrams) you need to put a ‘controllable switch’ in this loop. (you can have another one for the hot water (though I just leave mine ‘on demand’ all the time)
I have thermostats around the house but I don’t use any of them as thermostats just as sensors.
I use generic thermostats (in HA)
Basically you need to have 1 radiaor that is always open as a bypass (the heating technician / plumber will already have done this) ALL your other radiators have their own Danfoss ZWave valves, worst comes to worst the boiler will switch its self off on temperature return higher than x (whatever you set that to, so it’s safe.
If any of the Valves are ‘below temp’ switch on the boiler, switch off when above temp.
I set my thermostats by frost protection (minimum of 6° C at all times)
Doors/Windows open 6°C
House Unoccupied 14°C
House Occupied - depends on time of day
Day 17.5°C
Evening 19
Night 18°C
The occupied bit is notional, if ANYONE (from the house) is within 4 km the heating says ‘occupied’
It also depends on which room
Why bother heating bedrooms during the day
Why bother heating other areas at night
You choose, make up your own numbers times etc.
I reckon I can get away with just on-demand water. It’s a trade-off between the cost of pre-heating the water against the cost of the water that gets wasted because its too cold. I could rig up a recovery system for the waste-water and use it to fill water-butts of course.
I don’t suppose you know the model number of the replacement panel? The only one I can find is the mechanical panel: MT10
It’s a trade off yes, but the amount of water to start a boiler is about 8 litres, the rest is dependent on the pipe diameter and the length of run (so that will be the same whatever mode). Preheating the water happens all the time so the difference (in cost) is quite small.
I would recommend you set up the heating to have two modes, a central stat to run things and another from the danfoss valves (this allows you both a first step and a fallback).
Last year I saved 23% off my gas consumption (and only 4.5 % off my electricity ).
[I will keep an eye on the gas as that’s very subject to weather]
I have no idea of the part numbers, go to plumb centre and explain what you want.
Alternatively, I just went through the boiler schematics and made some wiring modifications (it’s out of warranty ! )
I don’t know the percentage but we saved loads when we automated our heating too. Just the simple fact of not heating an empty house makes a massive difference.
It’s actually probably my best investment, as the relay cost £2, the nodemcu was about £8, so I basically spent a tenner on smart heating and probably saved that in the first month.