Vaillant boiler overheating (F20)
Hi,
My boiler overheats after I had the heating on in a couple of rooms for a few minutes, even at 17-19 degrees. I don't know much about heating systems, it was installed by the a "specialist" during the house renovation.
The set up:
A new Vaillant ecoPlus 800 series, with Tado wired smart thermostats, in the loft.
I have 1 Tado thermostat right next to the boiler which seems to have to be switched on to control the smart valves of the 6 radiators that are on the first floor and loft. There is also 1 radiator in the hallway that has its original TRV.
On the ground floor, there are 2 Tado thermostats, 1 for each underfloor heating zone.
Any help as to why the boiler is overheating and what to do to solve this would be greatly appreciated! Thank you.
Comments
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The overheat sensor triggers when the water temperature exceeds the working limits of the boiler. If the water boils it will do significant damage. The cause will be insufficient flow of water through the heat exchanger. Likely faults will be a blockage in the heating pipe work, blocked heat exchanger or slow/failed pump. Assuming this is a combi? What happens when the hot water tap runs for an extended period of time?
Can be a number of issues, even a faulty heat sensor, so may be quicker just to get a heating engineer to diagnose.
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Thanks for your reply!
Yes this is a combi boiler.
I had a Vaillant engineer checking the boiler and he told me everything is fine with the boiler. I never had any problem when using (very) hot water. The error always happens when I am using the heating system.0 -
You could try removing one or more of the TRV heads which will ensure there is always a path for the water to freely circulate. In theory this shouldn't matter, because your boiler has an internal bypass valve. When all the radiator and UFH valves close the bypass should be forced open so that hot water circulates in a loop internal to the boiler. Your heating engineer should have calibrated the bypass valve in conjunction with the pump speed. The pump needs to create enough pressure to open the bypass valve. If the pump is too slow and the differential pressure setting on the bypass valve is too high, then the bypass will stay shut.
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I already have 1 radiator with its original TRV but I will try with another one, and talk to an engineer. Thanks for the help.0
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What is the heating system flow water temperature set to?
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It was 62 and the Vaillant engineer set it up at 54.
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There's definitely something up with it.
I'd probably try turning off all the zones but the one with normal radiators. Set that to a temperature about 2c above current and see what it does. Then turn off that zone and do the same with the others one at a time. That might show you there is an issue with some other part of the system that is effectively causing a blockage if it runs ok with only certain zones enabled.
If it's all of them there is a fundamental problem and you need a better engineer to come out.
What is the error on the boiler when it's over heating? Have all radiators been bled to make sure there isn't some daft air pocket?
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Just noticed the error number is the title, doh! 😀
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Really appreciate the help and guidance.
There is one thing I can't figure out and that's probably very basic but ... How does the boiler heat if I don't switch the Tado system on? In other words, how can I have the radiator with its original TRV (not a Tado) to heat if I don't turn on the Tado linked to the boiler? Do I just need to open the valve of the radiator?
I will try to do the zones test and replace a Tado valve by a normal TRV and give an update.
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I was just re-reading your original post. What do you mean by "I have 1 Tado thermostat right next to the boiler which seems to have to be switched on to control the smart valves"?
You shouldn't have to turn this thermostat on. I assume it will be acting as the zone controller for the smart TRVs.
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The installer installed this thermostat as a main control for the boiler. I can't seem to be able to switch the Tado valves on the radiators if this thermostat is off. In other word, it is like I had 3 zones in the house:
- Thermostat 1 : underfloor heating kitchen,
- Thermostat 2 : UFH living room,
- Thermostat 3 : The 6 valve radiators (first floor and loft).
Now I wonder... is this even how it should be?
If the "thermostat 3" is not needed, how do the valves talk to the boiler?
Hope a drawing helps to clarify..
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I suspect the Tado valves are setup as Independent, meaning they cannot call for heat from the boiler. If you want the valves to switch the boiler on then Thermostat 3 should be assigned as their Zone Controller. You will have to do this in the app for each room. If you did this you would then turn Thermostat 3 off - it has no role other than turning on the boiler when a valve is requesting heat.
Read this help page for info on setting up zone controllers. Make sure you use the correct device ID number.
I'm guessing at the moment thermostat 3 is forcing the boiler on when all valves are closed, which may be causing your problem.
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This is VERY helpful! I feel like we (you all more than me!) are getting close to solve this....
I read through this page (and others) and it seems that I should have the following configuration ideally.
Example C: a room has no Zone Controller assigned, so it is independent and won’t communicate with any Zone Controller. This setting is ideal if the room doesn’t belong to the Heating Zone that is controlled by the Zone Controller. For instance, this works in houses with different Heating Zones for radiators and underfloor heating. The Smart Radiator Thermostats do not communicate with the Smart Thermostat which is the Zone Controller of the underfloor Heating Zone only. Radiators and underfloor heating are controlled independently of each other in this example.
I can't seem to be able to make this thermostat a zone controlled without the help of a professional (this is what the app is telling me when I enter my boiler reference).
Can I just remove my Tado "thermostat 3" and control the valves independently or do I have to change the wiring to the boiler if I do that?
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You’re getting confused. You need the thermostat to make a connection with the boiler. The trvs will communicate with it, via the hub. You set the zone controller by going to settings > rooms and devices > click room > select zone controller under heating zone. You will want whatever thermo 3 is called. If that isn’t an option you will need to register that thermostat.0
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Looking at the example C (picture below) it seems that the thermostat is not required and the valves can individually communicate with the boiler. This is what I am trying to do.
To be fair, controlling the valves with or without thermostat does not make a difference to me as long as it works! :)
Anyway, I will try to delete then re-register this thermostat and see if it works cause I don't have the option to make it a zone controller for the moment.
I'll let you know the outcome....
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Think about it. How can the valves communicate with the boiler without something being connected to the boiler? That’s a very misleading diagram, I’m assuming in the text it says something about a wireless receiver being connected to the boiler.
Think you’re on the right track with getting the thermostat reregistered, if that doesn’t work you might need to involve Tado support.0 -
Your installer may have locked your configuration. You might need the help of customer support to unlock.
As you have a problem with the water circulation deadlocking I suspect you have a motorised valve on each zone, so what you pictured above may not be right. Your setup may have 3 wired thermostats wired to 3 motorised valves. Something like this:
If you look at the Zone Controller setting for Thermostats 1 & 2, are they set to themselves? Or are they set to thermostat 3?
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Each of them are set individually.0
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If it was my system I'd set thermostat 3 to be the zone controller for all smart TRVs, and then set thermostat 3 to off so it is unable to schedule your boiler on. Thermostat 3 being on when all TRVs are off is likely to be the cause of your problem.
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Ok, so I reset all 3 thermostats and they show as 1 zone each (zone 1, 2 and 3) and I have linked all the valves to the thermostat 3.
I hope everything will work fine now! Thanks a lot for all your help, it’s much appreciated.0 -
What do you mean by one zone each? Has your system not been set up for rooms? If not I would do so or you won’t be able to call for heat in individual rooms.
Thermostat 3 should be the zone controller for the trvs, the other thermostats should be zone controllers for your UFH zones.0 -
Ok now I am definitely confused. I thought each thermostat was a zone controller and the smart valves are linked to Thermostat 3. Did I misunderstand?
Result of my “new” setup… some radiators work and some don’t! And there isn’t any heat in the the rooms that have thermostat 1 and 2.0 -
The first thing you need to do is to set up rooms with the correct trvs in each - master bedroom, spare bedroom etc. All of these should be assigned to zone controller thermostat 3. Assign thermostat 3 a room that is different - attic for example.
Make rooms for the UFH too, living room, dining room for example. Assign the thermostats in these rooms to be zone controllers as per your diagram. Once you have done that, see if it’s working.
If there’s still a problem it may be down to incorrect wiring but there should be no reason why some trvs are calling for heat and some aren’t.0 -
Yes, this is what did and the boiler didn’t overheat!!
I have 2 radiators still not working (they were working previously) but at least I can warm the house up.
One more question…. Should the thermostat 3 (the one controlling the valves) always be ON or should it be ON when the radiators in this zone are ON and OFF when the radiators are off?
And should it be set to a low or high temperature by default?0 -
I don’t understand why your other radiators aren’t working - this sounds to me like there’s a blockage in the system. assuming the trvs are responding I would get it checked out. If it’s the trvs that aren’t responding there may be a connection issue or they may not be registered properly.
Is there a radiator in the room where thermostat 3 is without a trv? If so set it to the temperature you want. If there’s no radiator I would turn the temperature down or off as all your radiators have trvs, so there’s no need for it to call for heat. The thermostat doesn’t control the valves, the valves send a call for heat to the bridge, when then tells the thermostat to turn on the boiler.0 -
I will try to re-register the 2 valves that don’t work.
There is 1 radiator with TRV in a corridor where thermostat 3 is, so I will leave it to a fairly low temperature as it doesn’t need much heat there.
Thanks a lot for the help everybody!0 -
After a few days of working well, the boiler is doing it again!
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If it's a new boiler I'd be bothering the installer and Vaillant until it is fixed. There is clearly something wrong somewhere.
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Can you check that the app knows that Thermostat 3 and the TRV in the same room as it are actually in the same room, as in check the 'Rooms & devices' tab and make sure that they are grouped together. If not then that room with the boiler may be requesting heat without openeing the TRV.
None of this should really be a problem that causes overheating though, the ECOtec plus series has an internal bypass that is supposed to open and allow adequate flow. The boiler installer should have checked the bypass valve setting and pump speed when the boiler was installed but maybe the valve has failed.
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How can I group the TRV with the Thermostat 3? The TRV is not Tado so I have no control on it in the app. Also, I noticed that the heating does not follow the time / temperature scheduled. I basically have to do everything manually.
Are you aware of any company that can help (London area)? I contacted a couple but they don't reply ...
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