Very basic heating control...

[BigCol]

Morning folks, I have a very basic heating system; a combi boiler with no control for hotwater, and only a room stat for heating control.

So, my question is, can i replace the room stat with some other device (appliance module) that would allow me to control the heating via HS?

I have an RFX Sensor that is providing regular temp readings into HS - surely im halfway there?

Colin

[Wadenut]

You could... but the question is, "Is it wise, or safe to do so?", especially with a boiler. What if HS, for whatever reason, goes down; or the module you're using fails to respond? Would you want the house to overheat or, worse, freeze?
You'd be better off with a HS controllable thermostat. There are many choices out there; Z-Wave, X10, etc. I'm still using an RCX TXB16 (X10) which does a fine job. This way, if HS should happen to quit, the stat will still be able to control the temperature safely. Even so, it's wise to use a mecanical thermostat, set very low, in the circuit as a backup should the TXB fail for whatever reason during the winter.

[BigCol]

Wadenut, would i need both parts that make up the RCS TB16, or just the room stat part?

[mrhappy]

I wired my central heating first to a WS10 converted to have an on/off and manual override, then I got sick of the loud relay click of the WS10 (it even woke me up one night!) so just in the end put a 13a plug on the end of it and plugged it into an appliance module (one of the X10^2 ones, virtually silent), it has lasted me three years without any trouble.

You sound pretty much halfway there, I have a script which runs every couple of minutes checking whether the value from my temp sensor is greater/less than a set point contained in an ini file. I change this set point from the hs webpage/iphone/hstouch/sms message so I have reasonable control over it. If the outside temp is greater than 13 degrees it disables the system also. It keeps the temp with surprising accuracy.

You really need to look at how your system is wired, my old controller just had a mains input, a controlled output and from there a junction box that switched the gas valve to open and the circulation pump on so essentially just plugging it into the wall did the same job.

[Wadenut]

If you go with the TXB16, it comes as a set... The controller and Wall display. There may even be one for sale around here, or, I've seen them reasonably priced on Ebay. Mines been going for four years now without a hitch.

[BigCol]

mrhappy, do you have a combi boiler also?

[w.vuyk]

BigCol,

I have also a very simple setup for heating, a central unit with boiler.

I have a RFXOM receiver/transmitter and a RTS10 (mostly sold with a Digimax thermostat combination). I have placed the RTS10 on the thermostat wiring near the heater. The old thermostat is still in place set at a manual temp a bit higher as wanted (a backup in case the HS server goes down).
With a RFXSensor I measure temp in the living room and when it comes higher then a set temperature it triggers an event to switch the RTS10 to off. It can also respond to occupancy in the house (conditions in the events) and move to a lower temp depending to the time.

Maybe this adds to your ideas.

Wim

[mrhappy]

No sorry its a normal gas boiler, the principle may be very similar (im not a plumber though) for control or even simpler (might just even require a contact closure for demand/satisfied, which could be replaced with a X10 universal module). Probably best looking at what your system consists of or getting a manual for the boiler.

Have you seen this http://www.automatedhome.co.uk/Revie...ce-Review.html or http://www.automatedhome.co.uk/Revie...on-Review.html whilst they don't mention combi boilers it might give you some ideas.

I spose it also depends on what sort of interface you want, with some of the X10/RF thermostats they look very nice on your wall but they come at a price!

[mrhappy]

Bigcol,

Just had a look at a few manuals for some combi boilers (http://www.baxi.co.uk/docs/Baxi_Comb...structions.pdf and http://www.mikrofill.co.uk/images/PD...n%20Manual.pdf [the first couple that showed up in google]) and they seem to vary but don't seem impossible to get to work.

The Baxi as an example passes 240v through the thermostat which a universal module would not appreciate, the Mikrofill seems to suggest that no voltage goes through the thermostat connection. Either way I think an appliance module and a relay with 240v coil/contacts and you would be on your way to having HS as a thermostat - but this depends on your comfort level in dealing with mains electricity. Depending on how you wired it you could have whenever the appliance module is on then the boiler thinks that the thermostat requires heating and off is when it is satisfied.

Hope this helps..

[BigCol]

looks like ive got some more research to do, thanks all for pointing me in the right direction.

I'm sure i'll have some more questions in a couple of days!

Col