Do I really need 2 starter kits?

jjloose

I presently have a simple system: old Danfoss mechanical thermostat in the hall connected to a Danfoss controller with a hot water tank in the airing cupboard and heat provided by a simple on/off boiler in the kitchen.

It seems that with Tado if I want to control the hot water I must buy the *wireless* starter kit, but to replace the mechanical thermostat I need the *wired* starter kit. Do I really need both?

I tried with the wireless starter kit and the result was weird... The tado controller turns the boiler on and off, but the central heating pump was still controlled by the old mechanical thermostat. Strange!

So now I'm wondering if the answer is the wireless starter kit plus an additional wired thermostat. That seems wasteful since I then have no use for the wireless thermostat.

So is there a way to provide hot water control and a wired thermostat without buying other equipment I don't need?

Any clarity much appreciated!

Jon

GrilledCheese2

All you need is one wireless starter kit. The receiver replaces the Danfoss controller. The instructions from Tado normally tell you to remove the old thermostat and then bridge/link two wires - Live and Switched Live. You then mount the wireless thermostat in the same position as the old thermostat, or in your preferred location.

jjloose

Thanks for getting back to me. Helpful.

So you're saying I don't need a tado wired thermostat but can use the wireless one anyway if I modify the existing wired thermostat and then the central heating pump will be controlled by the tado too?

The instructions for the controller didn't mention the thermostat. Now I think about it I didn't go through instructions for the (wireless) thermostat (since it just connected fine) so didn't see any instructions about modifying my existing wall mounted thermostat. So, will there be step by step instructions for opening up the danfoss thermostat and connecting the right wires together? The step by step instructions for the controller, with sticker labels, etc, are excellent and I'd prefer that kind of support before potentially damaging the existing system!

Thanks,

Jon

GrilledCheese2

Yes, you don’t need a wired thermostat.

I suggest you install the receiver following the instructions and power up the wireless thermostat. Retain the old thermostat, but turn it up to the max temperature. You should then be able to use both the app and new thermostat to control the heating and hot water. The pump shouldn’t run all the time, only when hot water needs to be circulated.

Can you post the model number number of your Danfoss controller. Depending on the type you may not need to bridge the old thermostat wires. Either way, turning the old thermostat to maximum should allow you to test the new receiver.

jjloose

Thanks for this. The Danfoss is an FP715.

I installed the receiver and powered up the wireless thermostat (WT). When the old thermostat (OT) was on the central heating pump (CHP) would run, but I didn't observe the CHP turning on/off via the WT. What I found was:

1. Turn up setting on WT with OT off. Boiler turns on but CHP does not run.
2. Turn on OT. Pump starts to run.
3. Turn down setting on WT to turn of boiler. Boiler turns off, but CHP continues to run.

So I'm not confident that simply leaving the OT up enables WT to control everything OK. I could be wrong (especially if its normal behaviour for the CHP to run after the boiler has turned off), but I'm not confident.

At the moment I have reinstalled the Danfoss so that the heating continues to function as normal until I know precisely what to do next.

GrilledCheese2

I’m going to guess you don’t have a modern S Plan or Y Plan system and it’s probably an old C Plan system, which is gravity fed for HW circulation. You can verify this by confirming that your pump only runs when the heating is on. During the summer when you have HW only the pump does not run. If I’m wrong I don’t know what else to suggest.

If my assumption about a gravity fed system is correct you can follow this extract from section 6 of the installation guide. Blue LED setting.

jjloose

Pretty sure its a "Y". When I installed the Tado controller the instructions told me to check dip switch 2 on the back of the FP715, which can be set to either "pumped" or "gravity". It was set to "pumped". There is also a motorised valve on the system, so I had assumed the system is a "Y". I just checked by switching everything off after running Central Heating only without water. Then I turned on the hot water only and I heard the motorised valve move and the pump came on. So it seems like a Y. However, I'm not sure about the circumstances in which a CH pump is normally on. Is it only when the boiler is running? When should I expect it to be on/off?

I'm beginning to wonder if I just didn't test it carefully enough when the Tado was in place. Perhaps with the old thermostat on it would have worked OK. The thought of reinstalling it just to check is not so pleasant, but maybe I have to do that.

GrilledCheese2

If the motorised valve has three pipes connected to it then yes it could be a Y Plan. If it’s a single motorised valve with just two pipes then likely to be C Plan.

With modern gas condensing boilers the pump is normally controlled by the boiler, because there are times when the pump needs to run even though the burner is not alight and heating water. It’s for cooling down the heat exchanger. With older boilers that have cast iron heat exchangers the pump might only run when boiler is fired up.