Modulating Vaillant

MaxRebo

Hello

Just checking other peoples experiences with using the ebus system on the Vaillant boiler

I have a Ecotec plus 824 using the Tado smart thermostat linked to the EU wireless receiver

When getting up to temperature the system works perfectly but when it ticking over its firing for about 10 minutes at a reduced flow but then turns it self off for another 10 minutes in that time it goes into anti cycle mode, then on the display shows the rad and pump symbols S 0 code no heat demand and then fires back up and repeats this

Last night it was -1 outside on the app it had 2 flames showing all times but was doing above

Its keeping the correct temperature house does feel warmer but thought the idea was to not to keep stopping and starting the boiler

BOG73

Hi@MaxR@MaxRebo ! I got a Viessmann 100 B1KC combi and is doing the same as your Ecotec since I've first installed Tado about 1 year ago. My observation is: when set temperature is near by the set temp(-0.2 usually) the flame stop on boiler and is cycling on and on(pump running) for a certain time depending on heat loss,then flame start again till set temp has been reached or over with 0.1-0.2.After,the same scenario on and on and the only way for me to stop this cycling and starting and stopping the boiler is thru smart schedule,leave boiler to work and for max 1hour then set a lower temp or off and forcing the Tado to shut. In my opinion is a design fault,Tado didn't take in the account this functionality of the P.I.D controller wich Tado software are based. I am not a tech but when people want OpenTherm,they expect a clean functionality and not something that is annoying. If i want 20°c in my room,start at 19.7 ,go slow and increase flow accordingly or go lower with the flow if temp raise too much,stop at 20.1-20.2 and no one will complain if the flow was 38C or 40C and slightly over to 20.4C . The only way is to ditch OpenTherm and go with relay connection on Tado and use an external sensor and Weather Compensation. The boiler will act normal,no on and off all the time and cycling 24h/day,Tado will not be in control. You may also use smart schedule and cut it off after 1-2 hours or whatever time you want to be on and off,but don't leave the same temp 24h cause it will be annoying.This in case you want to keep it on digital opentherm. Also,set back temp to 0.5-0.7 to your desired temp in a time slot,depending how much heat your house is loosing in 1-2-3-4 hours as a reference to your time slot between heat on and heat off schedule.Maibe this will help.

Rodgerq

Is it possible your boiler is over sized and unable to modulate low enough to maintain a steadier flame? I think I have the same issue with my WB, although not now that it's below freezing outside). Earlier in November when temps were around 7 it would be on and off a lot more.

BOG73

Not the case,even though is a 35kw boiler with a min output of 6kw,i got 13 radiators in total,6 of them quite big(33 type 1600x 600),boiler running at 34C to 45C most of the time when heat demand is over 30%. Lower then 30% and differential between set point and set back are lower then 0.5,the boiler will get only on/off signal from Tado and pump running(cycling).I have to use the smart schedule and give a large amount of time (3-4 hours) to let the temp drop more then 0.5C and not have the on/off scenario for 3/4 hours till temp drop enough for Tado run properly. In my opinion,Tado should have in Tado Installer App an option to choose the lowest point between set temp and set back temp where the boiler to actually fire and not cycle so much,like it happend to me. Have 0.7°c-0.8°C differential between starting boiler and stop the boiler with advantages of modulating and that it is and all I wish to have....why to fire boiler 2 sec then stop and again and again till temp drop...Tado has put too many variables in this equation and should give more possibilities to customers for fine tuning acording to their house specifications.Make Tado more flexible for us and if we f@#$ up all is needed is a button with factory reset.

eezytiger

@MaxRebo I have an EcoTec 831 Plus and it functions as yours. I've tried eBus three times in the last year and each time I've turned to relay control. The problem is that the boiler is far too powerful, even at minimum output. It is impossible for the boiler to maintain a steady, low temperature unless your heat loss exceeds boiler output. With too much power the water temp just rises and rises until, eventually, the only option is to shut down.

My home needs 5 kW in the worst conditions. Right now (currently 0C at 09:00) 4 kW is sufficient throughout the night and day. My boiler minimum is 9 kW. It is impossible to keep it running low and slow all the time. It will simply overheat. eBus won't help. I need a bigger house, colder climate or, a more modern boiler designed for these enlightened times.

MaxRebo

Thanks for the replies

Been using the ebus system now for a week and its been very cold outside for that week

House does feel warmer, not using anymore gas, heating is quieter as its staying warmer and keeping house temperature better, I suppose the down side is the ignition is being used more

I did email Tado who replied this is the way Tado works but they could change the algorithm to prolong the on off heating cycles but this could have consequence with the way Tado heats meaning it could heat above the target temperatures

Think I will keep it as it is and see how it goes especially when its not freezing every evening

chatmandu

@MaxRebo  "I did email Tado who replied this is the way Tado works but they could change the algorithm to prolong the on off heating cycles but this could have consequence with the way Tado heats meaning it could heat above the target temperatures"

Did they offer to change it just for you as a custom job?

That might be quite a handy feature - e.g. when maintaining temperature, wait x minutes from last burn or temp drop of 1C, whichever comes first, then burn on minimum power until target is reached

My boiler has a minimum output of 6kW, but I'm only using an average of 4.6kW of gas during the UK's current cold spell (3C during day / minus 3C at night).

I've ordered the EU version of Tado v3+ (ebus) to replace a Honeywell T4R (relay). The Honeywell seems to be fighting the boiler. Despite having a max flow of 60C configured, and the thermostat being 2C below target temp, the boiler keeps cycling/pumping/anticycling instead of performing a longer low powered burn - this despite the flow temp being in the low 40s.