New to tado zone controller question on single zoned system

Mintimperial

hi and thanks for taking the time to read my post and any help appreciated

as Far as I can tell my combi boiler operates on a single zone. I have installed the v3 wireless system with 4 smart trvs.

I have an open plan house and have tado valves on rads in master bedroom, daughters room, dining room and living room, the wireless thermostat is in the Livingroom and tado reflects those rooms. Dining room and Livingroom separate. There are 8 rads in total in the house.

In the app all trv are linked to wireless controller in app. All other rads have dumb trv.

Conclusion my system min power is 3kwh and want to control heating in master bedroom, daughters room and Livingroom independently.
however to maintain the minimum power the Livingroom trv is always on with the other rooms

Eg living room = Livingroom and dining room

Master bedroom = Livingroom and master bedroom

Daughters room = living room and daughters room

I am not using the schedule yes and have set scenes in HomeKit to activate the heating in those rooms I want to heat and turn off.

My question is do I need a second wireless thermostat to manage the upstairs master bedroom and daughters room or is there a different set up that will achieve the intended result without having issues with the boiler.

Thanks in advance for any help / advice

policywonk

Going through the basics. As you describe it, there are seperate radiators for each room and you want to keep demand down and handle it efficiently. Before thinking about homekit- which I know nothing about, this is what presents in my mind:

1. Ensure that all rooms have room specific wireless (either wall sensors, or smart TRVs) thermostats in place, so that temperature by time of day can be set and focused to reflect every room's specific, individual usage.
   1. You dont have to replace all your radiator valves in one go- at least make sure that the rooms which have significant usage have dedicated thermostats, leaving the other rooms with their radiators trimmed down to handle the overspill.
   2. Note: you will find, when you've been monitoring demand over at least a month, that rooms on lower floors handle a considerable component of the heat which the rooms above actually need, convection through the floors is more impactful than we may realise.
2. Ensure that the temperature timetables for each room are well organised, reflecting likely time-of-day temperaure requirements. Refine these over many months.
3. If your pump is more than 10 years old it is likely you will benefit from replacing it with a smart pump that either offers a constant differential pressure, or a constant pressure, not just a constant speed! This will enable heating to be more effectively and economically distributed through the home - and a Tado system will be more impactful on costs.

Hope this stimulates your thought process.

eezytiger

@Mintimperial If I understand what you've written you are keeping the living room radiator on whenever heating is required elsewhere simply so that the boiler can run continuously at 3 kW output. Why does the boiler have to be kept running? Why can't it cycle on and off periodically?

In the UK this past week my average heating demand over each 24 hour period, with heating on 24x7, just happens to be 3 kW or a smidge under. Unfortunately the minimum output of my boiler is 9 kW. The boiler has to cycle on and off. There is no other option.

policywonk

@eezytiger @Mintimperial the reason why I suggested installed a smart pump with potentially an automatic bypass valve was because these two additions do pay for themselves within 2 years when added. They reduce the incidence rates of the boiler thermally cutting out when the flow rates cant keep up with boiler output.

What are your boilers? Can they be modulated on digital controls, such as Opentherm, EMS-BUS, etc? Have you investigated that?

eezytiger

@policywonk My boiler is a 14 year old Vaillant EcoTec Plus 831. Minimum CH output is 9 kW and I've already range rated it down to the minimum. Max is 24 kW for CH.

I have a permanent bypass radiator in the hall, with the smart wired thermostat. Also, at present I have three other radiators with the SRTs fitted loosely, effectively acting as additional bypass radiators. Only the lounge can call for heat. All other radiators are independent and can only passively receive heat when the lounge calls for it.

I've tried eBus on two separate occasions, but it is pointless, because the boiler flow temp rapidly exceeds the set flow temp (e.g. 33C) and shuts down, sometimes within less than a minute, before any useful heat has escaped into the radiators. Then the pump runs on for five minutes, doing nothing except wasting electricity. And then the anti-cycling timer stops the boiler firing up again for several (20?) minutes. It is absolutely hopeless. Therefore I'm using relay switching with a minimum 10 minute burn time.

Flow temp is set manually to 50C and the boiler will shut off once it reaches 53C. This is the way I've set the system up for, IMHO, best efficiency and efficacy given that the radiators are 36 years old and sized for a non condensing boiler with no restriction on flow temp.

I would love a boiler with a 2 kW (or even less) minimum output, but since there is nothing wrong with mine other than the specs I will stick with it till it needs replacing. Hopefully another ten years or so. It's been extremely reliable so far, only needing the diverter valve replaced, once. Otherwise no attention whatsoever in the last ten years except a service when the diverter valve was replaced.

policywonk

@eezytiger Just spoken to a colleague who services these boilers in the city (they have natural gas there). He immediately understood the problem and suggested you talk to the Vailant team that services your boiler it, asking them to consider fitting a different gas flow restrictor. It would reduce the amount of natural gas going into the combustion chamber. According to him, whilst many models share a similar chamber, the flow restrictor determines the gas throttle range. He said that Vaillant know how to change the gas flow restrictor. Sorry this is above my head, perhaps this is something Vaillant can advise on.

eezytiger

@policywonk Thanks for the suggestion. I will follow up on it. I assumed the spec sheet was the spec sheet and nothing could be done.

The most gas I've ever used on the coldest winter day is 120 kWh (years ago, before insulation improvements) or just 5 kW averaged over the 24 hour period.

Christ knows who thought that designing a condensing boiler with a minimum output of 9 kW was the right thing to do. I wonder what they're doing for a career now. 😉