Why is Tado overshooting the temperature setpoint?
Hello,
I have a Saunier-Duval ThemaPlus Condens (Gas condensation modulating boiler). Its max flow temperature is set to 60 C. Tado has been installed for more than a year.
I don't understand the temperature in some rooms (with TRVs) overshoots the setpoint by a lot!
The graph shows that a 17:30, the boiler starts heating very strongly, and it reaches 19.9 C around 18:30.
- Why is it overshooting so much (it's been installed for a while)
- Why is the TRV requesting strong heating (the boiler is modulating and configured with OpenTherm, so it could heat slowly over that period of time).
Anyone has any clues?
Thanks!
Bruno
Answers
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Additionally, here is the temperature in the afternoon:
The temperature oscillates between 16 and 19 degrees, this is just crazy!? (the setpoint is 16).
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You can see that Tado actually closes the valve but the room continues to heat for quite a while after. This would suggest that your radiators are perhaps oversized for the room so even once the valve is closed, it's still full of hot water and that heat will radiate into the room.
Later on, the valve only opens partially so the spike isn't nearly as pronounced.
Are you using early start on your TRVs? If so, don't bother as it just doesn't work.
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Try turning down the boiler flow temperature.
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Thanks for you replies.
I don’t think the radiators are oversized. The room is quite big. My understanding would be that Tado would learn that if it heats that much it overshoots, so it would heat a bit less the next time. Also the boiler is a modulating boiler so it could heat with less power for longer rather than heat a lot for a very short period of time, no?
My boiler flow temp is 60 degrees. Isn’t that normal for such a boiler? Do you recommend lowering it further?0 -
Larger radiators can handle lower flow temperatures and still heat the room. It'll just take a little longer. We have 1980s rads in our relatively poorly insulated Edwardian house (high ceilings and some single glazing). Flow temp around 55C today. House still holding temp, but boiler is running pretty much 24/7.
TBH, I'm not convinced tado is actually that smart. I've been running it for 10 years and it still doesn't seem to know our house.
If your boiler is modulating, then that means it'll pare back the burners to maintain the set flow temp. Mine has weather compensation, so also automatically varies the set flow temp based on the outdoor temperature, rather than me manually making seasonal changes.
Try it on 55C at the moment. It might address your overshoot and also give you some gas savings. May take longer to heat up, so account for that. If you find the rooms are warm enough, your rads aren't big enough for the flow temp.
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If your boiler is modulating, then that means it'll pare back the burners to maintain the set flow temp. Mine has weather compensation, so also automatically varies the set flow temp based on the outdoor temperature, rather than me manually making seasonal changes.
Well, actually, it's an OpenTherm modulating boiler, so Tado should be able to modulate the temperature in the pipes. TBH if I switched to Tado I was expecting to avoid an all-or-nothing situation, which is kind of what we have here.
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So with OT, you're running a form of load compensation - indoor reference point determines and adjusts flow temp of boiler, which modulates the burners accordingly.
The effectiveness of LC and WC largely depends on the characteristics of your property. WC tends to suit older, brick built properties with higher thermal mass but lower insulation levels, whereas LC suits newer properties with lower thermal mass and higher levels of insulation.
WC is more proactive (before the temp difference is felt inside), whereas LC is reactive to changes registered inside. This usually causes more frequent aggressive changes in the flow temperature for LC than for WC and it's possible what you're experiencing is the LC swiftly increasing the flow temperature to hit target, target being reached, but then of course, as @davidlyall says above, the rads are then pretty warm, and so the temp keeps going up, even though the valve has closed back.
Do you have a room (wall) stat too? Due to being on the rads, and in the UK that being typically at the bottom, vertically (as opposed to the top, horizontally in most of Europe), TRVs are not really going to give an accurate room temp. Tado's wireless temp sensor supposedly addresses that, although of course most people aren't delighted with having to buy more kit just for their valves to work as they'd hoped.
You will likely reduce overshoot if you reduce the flow temperature. I believe that's possible with tado OT, but as I don't use it, I can't tell you how.
If you need the higher flow temperature, you can alternatively try balancing down the 'offending' radiator so it doesn't heat up as fast/so far.
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Oh, one other thought.
You'll also get faster increases in temp swings going from a cooler start. If your rad is off and the room is 16C (which appears to be the case), then the heating comes on with a circa 60C flow temp, that will always make a pretty quick difference to your room temp.
Our lounge has higher heat loss than our hallway. Tado (wall) stats in each. Lounge usually heats much more rapidly than the hallway, as it's coming in from a lower starting point. Lounge then cools faster too (higher heat loss), which is why we have two room stats.
I'd certainly be having a look at the balance of the rads over your system, along with the boiler flow temps.
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Thanks for all this knowledge. I'll try to let that sink in.
- I'm actually in France, the TRV is on top, horizontally.
- Our house is in stone but has been refit with fairly good insulation. It's true that these are room where I'm trying to keep the temperature fairly low (16 C) because that's fit for us during the day when they are empty or even at night when we're sleeping. I just want to bump the heating around bed time etc.
- It's also true that I don't see this behavior in the living room where I'm more consistently requesting a temperature of 17/18 C.
I guess what I don't really understand is why Tado doesn't learn that it could just keep the valve slightly open in these rooms and get some heating to keep the temperature more stable, especially at the boiler is already heating the living room at those times.
I'll give a try at reducing the heat flow temperature a tad bit
I'm a bit unsure by what you mean when you mention balancing down the offending radiator?
Last, @davidlyall mentioned deactivating Early Start. Is this something that could cause this issue?
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Looking at the duration and intensity of the heat in the graphs I'm surprised to see such a sharp increase in room temperature. @DM932187 commented on using a wall temperature sensor for more accurate temperature measurement. If not already done so, I'd suggest using a cheap digital thermometer to measure and track the actual room temperature. I suspect the temperatures reported by the TRVs are inaccurate when the radiators are heating up.
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Are you familiar with UK radiators? They have a valve at each end. On has the TRV and the other tends to have a cover on it which can be unscrewed to reveal a valve that will (like the TRV) adjust the flow to the radiator. Turning it clockwise reduces the flow, and anti-clockwise increases the flow. The aim is that across all of the radiators in your system, they are all 'balanced' so that they each heat up at around the same pace, and reach and maintain the target room temp. There is a good article on balancing on heatgeek.com
If your system is already on when the offending rad's TRV opens, that will exacerbate the temperature swing, as it's swiftly going from cold to full flow temp. If you were running a dumb TRV on this rad (at a fixed set point) this wouldn't happen. It would restrict the flow to maintain its set point. Dumb TRVs don't usually fully close down unless you turn them off. Which is, of course, what you're also expecting from tado's smarts.
There's been some discussion in another thread on here about 'graduation' of the tado TRVs and whether they are simply on/off or open/close in stages. I believe Tado confirmed it's the latter, but your experience suggests otherwise. That said, you may be finding at 16C the tado valve is off, then to move towards 18C, it fully opens. I can't tell you why it doesn't then partly close. Is the TRV set to call for heat, or is it merely acting as a scheduled dumb TRV (i.e. depends on the call for heating coming from a central location - e.g. room stat in a hallway)? Logically, the latter might work better in your situation but you'd need to try both and see which works best.
@davidlyall's reference to Early Start possibly relates to the general consensus that it doesn't really work with TRVs. It's better with slow response systems. That said, I don't use it with mine (which is slow start), preferring to schedule a manual ramp up (gradually increasing the set temp over periods of time), which works very well.
Hope that helps.
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What a thorough reply, very interesting. Thanks! I'll try lowering the flow temperature and keep you updated.
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I don't know if I can compare apples to apples because it was slightly warmer on December 13. Still, it was an improvement to reduce the water flow temperature to 55 C. Tado seems to behave more reasonably by requesting heating a little continuously rather than creating spikes. It's even successful at keeping the temperature right around 16 C if you look between 14:00 and 17:00.
It's still overshooting a lot at 18:00 where the setpoint is 18 C but it overshoots to 19.6 C.
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Good stuff. Try slightly turning down the flow to the spiking rad and it won’t get as hot so won’t continue to heat for as long after the call for heat ends.0
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I wish I could do that, but I'm in France, and we don't have the two valves on our radiators, just one, and it's equipped with the TRV.
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