Any savings using eBUS when minimum boiler output is 7kw+
Has anyone gone from using eBUS back to using relay mode where their boiler is simply to powerful for the rooms they are trying to heat?
The issue I have is my boiler is realistically too large for my central heating requirements (probably the same for most combi's fitted in the UK)
My heating demand for the whole house is only around 11-12kw. My boiler (Vaillant Ecotec 938 combi) has a minimum output of 7kw. As I have Tado TRV's on the majority of radiators I find I need far less than the 7kw of power even on cold days once the house is up to temp.
I am finding the boiler simply doesn't like being told to run at 35-40oC and will get to that temperature very quickly and then go in to anti-cycling mode. I already have my boiler set at 55oC flow temperature within it's control panel (so even when Tado requests 75oC the boiler will not output this, as my house can get to temp at these lower temps).
Makes me think my setup might actually be more efficient in relay mode as at least it will try to heat up to 50-55oC giving off something for the gas it has burned, rather than at the moment where it will cycle lots of times until temp drop too far.
It seems to me like this might be why Tado moved to only having relay mode in the newer kits as the bulk of commonly fitted boilers up until very recently cannot range down low enough to make the Tado product worthwhile. The only way I can think to get 35-40oC to work was by running all the radiators in each room rather than specific zones (but then I think the efficiency saving would be outweighed greatly by burning gas to heat the un-needed spaces). Anyone any views / had same type of thing?
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I've come very much to the same conclusion. I have 9 rads with 8 Tado SRTs, fitted in October 2021, so almost a year ago and for one complete winter season. My boiler is a Vaillant Ecotec 831, which has a minimum output of 9kWh.
I have twice tried setting the system up using eBus and twice I have given up and returned to relay operations.
With eBus there have been demands from Tado as low as 33C flow. That's absolutely useless. The boiler fires up for, at most, 30 seconds, before shutting off the gas and then proceeds to overrun the pump for several minutes with no new heat in the system. It's a complete waste of energy and pointless boiler stress. This continues until there is enough heat deficit in the house that Tado finally asks for a sensible flow temperature and something approaching normal behaviour returns - until the next time.
So, it's back to relay control and manual adjustment of flow temperature to maintain the lowest return temperature that I can.
By the way, due to the oversized boiler I have range rated it down to the minimum heating output of 9kWh. The heating is on, to varying degrees, 24x7, as the house is almost always occupied, so there is never the need for an urgent and rapid heat boost such as when returning home from work. In fact our style of boiler operation is closer to that of a heat pump, keeping it low and slow.
Furthermore, I tend to keep most of my SRTs in independent mode, with only the most critical rooms able to force the boiler to come on. In this way I hope that, instead of trying to disperse 9kW from just one or two radiators at a time, there will be several radiators needing heat when a zone controlling radiator needs it. It's a bit like the good old days of a single thermostat in the hall controlling the boiler, but now I can pick as many rooms as I wish to command heat and, of course, I have accurate SRTs/TRVs (instead of 8 failed TRVs) that can have temperatures and schedules fine tuned to perfection.
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Cheers for responding. Sounds like you have the same challenges I have with the system and performed the same action.
I range rated mine down to 11kw in coldest months (and change to 7kw in Autumn). I also only set the living room to have the ability to call for heat (and sometimes my office). I have the other 12 TRV's set to independent with just a temperature set point and no direct heating control.
Basically I have come to the conclusion that this system hasn't really worked too well for my property as I'd almost get a similar setup with a regular controller and just manual TRV's. The only benefit gained is having the bedrooms set down in the day and up on a night.
I am wondering if Tado can set a minimum heating amount, as i see reports on here that they can set a maximum heating temperature. I've just dropped them an IM to see.
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Tado say they cannot set a minimum flow temperature, however they also said they can’t set a maximum (which we know they can), so not sure I believe.0
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I don’t know who at Tado told you they couldn’t set a maximum flow temperature but they definitely can, with Opentherm at least, don’t know about ebus. As for minimum flow temp, not sure if there’s an Opentherm command for it.0
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Hi. I just bought a tado to get remote control of my home, which is heated by a 30kw Bosch fuel heater. This in itself is only regulated on or off based on the water circulating in the primary system. Actuall temp control is made using a 3 way valve. I bought an analog 0/10v servo from Siemens and will try this setup. I hope tado pid will be able to manage a nice progressive valve control while still having the Bosch heater running in tor mode avoiding the issues you have…0
