Complicated? Opentherm or on/off

[david007]

Sorry to trouble you but I wondered if one of you genius out there could help with some technical advice?


I have a Vokrea i36 Utica (of which I am very pleased it’s a nice piece of kit). It is classed as an opentherm boiler. Additionally it modulates on a 10.1 ratio.


Now. I have it wired to a nest 3rd generation thermostat. Currently it is just wired to on/off however I am led to believe that it should be wired to opentherm and NOT on off. What I am slightly confused with is that if the temp of the boiler (heating) is set within the while settings it is in modulating mode. As I result I fail to see why setting it up to opentherm would make any difference?


I am assuming that opthetherm in the back slowly condensing and keeping the rads as a lowest temp but maintaining the temp of 20 degrees for example. Surely is that not what modulating does?


SO should it be rewired to opentherm and no on and off? The object is to save money on fuel (gas). However it seems counter intuitive to have boiler running all day even when it running on a low temp?


Please forgive the question as what may seem simple to one is very complicated to another!


Finally Vokrea and Nest seem a little clueless

 

[david007]

Diagram

 

[rpm]

Do you want the same answers posted to both sub forums or just the one?

 

[david007]

Do you want the same answers posted to both sub forums or just the one?

Just the one thanks. My rationale is that some may not look at differing forums

 

[Riley]

One posting is ample otherwise it may be seen As spam

 

[david007]

Apologies, which is the best to post on?

 

[Riley]

Either would’ve been fine don’t worry all new postings show up so we can see them

 

[david007]

Either would’ve been fine don’t worry all new postings show up so we can see them

Cheers mate

 

[doitmyself]

I am assuming that opthetherm in the back slowly condensing and keeping the rads as a lowest temp but maintaining the temp of 20 degrees for example. Surely is that not what modulating does?

Modulating does not maintain the room temperature - the room stat does that - it tries to maintain the required flow temperature. If you have an on-off thermostat the required flow temperature is constant, say 75°C. When it is very cold outside and the room is also cold the radiators need to give out the maximum heat, so a flow temperature of 75°C is required. But as the room warms up the radiators do not need to give out as much heat. If you have an on-off thermostat, and fixed flow temperature, the return temperature will rise. this causes the flow temperature to also rise above the desired 75°C. So the boiler shuts of until the water temperature has dropped. And the cycle repeats itself.

If you have an opentherm controller, this compares the actual room temperature with the desired temperature and instructs the boiler what flow temperature to use. If the difference is high, the required flow temperature will be high; if there is a small difference between desired and actual the required flow temperature will be lower. (I am assuming that there is no external temperature sensor.) As the room temperature rises the flow temperature will decrease.

 

[david007]

Modulating does not maintain the room temperature - the room stat does that - it tries to maintain the required flow temperature. If you have an on-off thermostat the required flow temperature is constant, say 75°C. When it is very cold outside and the room is also cold the radiators need to give out the maximum heat, so a flow temperature of 75°C is required. But as the room warms up the radiators do not need to give out as much heat. If you have an on-off thermostat, and fixed flow temperature, the return temperature will rise. this causes the flow temperature to also rise above the desired 75°C. So the boiler shuts of until the water temperature has dropped. And the cycle repeats itself.

If you have an opentherm controller, this compares the actual room temperature with the desired temperature and instructs the boiler what flow temperature to use. If the difference is high, the required flow temperature will be high; if there is a small difference between desired and actual the required flow temperature will be lower. (I am assuming that there is no external temperature sensor.) As the room temperature rises the flow temperature will decrease.

Thank you, there is no external sensor, just Nest (google location) temp. Sorry to be dim but if opentherm is installed then surely if the boiler is going to conflict on modulation mode? Is there much difference really between the to or just preference? Im struggling with this!

 

[dancinplumba]

the OT stat tells boiler what to do

 

[Old Account]

Sorry to trouble you but I wondered if one of you genius out there could help with some technical advice?


I have a Vokrea i36 Utica (of which I am very pleased it’s a nice piece of kit). It is classed as an opentherm boiler. Additionally it modulates on a 10.1 ratio.


Now. I have it wired to a nest 3rd generation thermostat. Currently it is just wired to on/off however I am led to believe that it should be wired to opentherm and NOT on off. What I am slightly confused with is that if the temp of the boiler (heating) is set within the while settings it is in modulating mode. As I result I fail to see why setting it up to opentherm would make any difference?


I am assuming that opthetherm in the back slowly condensing and keeping the rads as a lowest temp but maintaining the temp of 20 degrees for example. Surely is that not what modulating does?


SO should it be rewired to opentherm and no on and off? The object is to save money on fuel (gas). However it seems counter intuitive to have boiler running all day even when it running on a low temp?


Please forgive the question as what may seem simple to one is very complicated to another!


Finally Vokrea and Nest seem a little clueless

Are you an engineer ? Are you allowed to wire into the boiler ?

 

[david007]

Are you an engineer ? Are you allowed to wire into the boiler ?

NO I am not an engineer and no I am not going to be wiring it. There was no suggestions I would be doing anything to it. It has been wired up by a nest installer, but I have learned that it could be wired up via an opentherm system.

 

[david007]

the OT stat tells boiler what to do

Does the nest do the same??

 

[dancinplumba]

Does the nest do the same??

is your Nest OT ?

 

[dancinplumba]

how do you know it's only wired to on/off ?

 

[david007]

is your Nest OT ?

Nest Thermostat

 

[david007]

how do you know it's only wired to on/off ?

i checked with the nest guy who installed it. its the basic set up.

 

[david007]

how do you know it's only wired to on/off ?

 

[david007]

Modulating does not maintain the room temperature - the room stat does that - it tries to maintain the required flow temperature. If you have an on-off thermostat the required flow temperature is constant, say 75°C. When it is very cold outside and the room is also cold the radiators need to give out the maximum heat, so a flow temperature of 75°C is required. But as the room warms up the radiators do not need to give out as much heat. If you have an on-off thermostat, and fixed flow temperature, the return temperature will rise. this causes the flow temperature to also rise above the desired 75°C. So the boiler shuts of until the water temperature has dropped. And the cycle repeats itself.

If you have an opentherm controller, this compares the actual room temperature with the desired temperature and instructs the boiler what flow temperature to use. If the difference is high, the required flow temperature will be high; if there is a small difference between desired and actual the required flow temperature will be lower. (I am assuming that there is no external temperature sensor.) As the room temperature rises the flow temperature will decrease.

I think may be getting confused with modulation and the SARA (in the diagram) function?

 

[dancinplumba]

View attachment 35224

that's done by a nest installer ? poor

 

[gingalig]

is your Nest OT ?

Nests are OT, no reason to wire them up any other way, if the boiler is OT.

 

[doitmyself]

but if opentherm is installed then surely if the boiler is going to conflict on modulation mode? Is there much difference really between the to or just preference?

the OT stat tells boiler what to do

The OT stat calculates the required flow temperature and sends this information to the boiler. The boiler then modulates the boiler to maintain the required temperature.

To quote the Opentherm Protocol:

The slave (boiler) does not need to know how the master (thermostat) has calculated the control setpoint (flow temperature), e.g.whether it used room control or OTC, it only needs to control to the value. Likewise, the master does not need to know how the slave is controlling the supply.

The boiler controls the flow temperature by modulating.

 

[david007]

Nests are OT, no reason to wire them up any other way, if the boiler is OT.

Why is there OT1 and OT2 setup?

 

[doitmyself]

Why is there OT1 and OT2 setup?

T1 and T2 provide 12V power to the thermostat, which communicates wirelessly with the Heatlink.
OT1 and OT2 carry the digital signals between Heatlink and boiler.