How does my boiler know when my rooms are heated to 20C?

[vagrantly3893]

I have a VAILLANT ecoTEC plus VC 20 CS/1-5 and each of my radiators has a TRV. I also have an outdoor temperature sensor that communicates with the boiler.

I understand that when the TRV is set to 3 and the room reaches a temperature of 20C, the TRV will prevent hot water flowing in to the radiator and instead flow to the next radiator. When all the TRV are closed, I assume the hot water bypasses all radiators and returns to the boiler. The TRV are not connected to the boiler, and I have no thermostat in the house that is connected to the boiler. How then does the boiler know that all the rooms are heated appropriately and that it should turn off?

Should I buy a separate Thermostat and place it in my living room?

[SteamyTea]

I don't know the model of boiler you have but suspect that it senses both the flow and return temperatures, if there is not much difference, then it shuts down.

It may also do this on flow pressure, which probably increases.

 

Is your boiler actually giving you problems?

[vagrantly3893]

16 minutes ago, SteamyTea said:

I don't know the model of boiler you have but suspect that it senses both the flow and return temperatures, if there is not much difference, then it shuts down.

It may also do this on flow pressure, which probably increases.

 

Is your boiler actually giving you problems?

It's only recently installed and we haven't used it for heating yet. I was just hoping to get some understanding about how the system works.

[Temp]

My understanding is that when all TRV are shut I believe the increase in pressure causes a bypass to open. This routes hot flow back to the boiler return. The flow temperature rises until the flow stat in the boiler shuts off. The boiler will eventually cool and light up again. 

[Conor]

I thought it was compulsory to have at least one central thermostat control alongside TRVs under building control regs?

[JohnMo]

Boiler doesn't know or need to know what occurs downstream, all it manages is temperature and delta T.

 

So the basis of operation is.  There is a target max temperature and a corresponding dT. The boiler will in a controlled manner increase flow temp in response to a change in dT. The dT being the difference in flow and return temp.  The flow temp will increase to the max it is programmed to do. It then stops. Once the return temp has dropped the process starts again.

 

Now a couple of questions for you.

1. You have an outside sensor,  is your boiler set up to run weather compensation?

2. Combi or system boiler?

 

 

[vagrantly3893]

15 minutes ago, JohnMo said:

Now a couple of questions for you.

1. You have an outside sensor,  is your boiler set up to run weather compensation?

2. Combi or system boiler?

 

 

That was a very clean explination, thanks.

 

1. I wasn't there when the engineer set it up, my wife was, however I would have to assume yes it is.
2. System boiler (it has a hot water tank)

Edited August 30, 2023 by vagrantly3893

[ProDave]

Without a thermostat anywhere what can happen is all the TRV's shut down, and the boiler and pump keep running to circulate hot water around completely pointlessly, and waste a small amount of gas firing up occasionally to keep that water hot.

 

The traditional way was one room did not have TRV's instead that room had a room thermostat.  That needs to be the room that takes longest to heat up, so you can be sure the other rooms are warm before that turns off.

[vagrantly3893]

1 hour ago, ProDave said:

Without a thermostat anywhere what can happen is all the TRV's shut down, and the boiler and pump keep running to circulate hot water around completely pointlessly, and waste a small amount of gas firing up occasionally to keep that water hot.

 

The traditional way was one room did not have TRV's instead that room had a room thermostat.  That needs to be the room that takes longest to heat up, so you can be sure the other rooms are warm before that turns off.

 

The original offer however did have a room thermostat, however the engineer made no mention of it during set up: https://www.vaillant.co.uk/for-installers/products/sensocomfort-sensocomfort-rf-72192.html

[JohnMo]

1 hour ago, vagrantly3893 said:

That was a very clean explination, thanks.

 

1. I wasn't there when the engineer set it up, my wife was, however I would have to assume yes it is.
2. System boiler (it has a hot water tank)

So if set to weather compensation, and you are on a system boiler, you should have two different flow temperatures from the boiler, one for cylinder and one for house heating.

 

So on cylinder heating, a high fixed output temperature and a lower variable flow temp for the house heating.

 

WC flow is running the boiler at the lowest output temperature to get the highest efficiency. To stop short cycling of the boiler you NEED an open system.

 

So WC should operate as an open system, i.e rad stats should be moved to say 23 degs if your room target is 20.  If the room or all rooms are getting to hot or not enough the WC curve is not adjusted correctly and will a require a tweak. Read the manual on how to make adjustments.

 

If the odd room isn't correct but the rest are ok only the flow to that rad needs adjusting.  Go on heat geek website and read up on system balancing, for what to do if this is the case.

[JohnMo]

27 minutes ago, vagrantly3893 said:

 

The original offer however did have a room thermostat, however the engineer made no mention of it during set up: https://www.vaillant.co.uk/for-installers/products/sensocomfort-sensocomfort-rf-72192.html

 

Did the senso comfort get installed?

[vagrantly3893]

1 minute ago, JohnMo said:

 

Did the senso comfort get installed?

My wife (who was there during setup) said the engineer made no mention of it, only the outdoor temperature sensor and that he programmed the heating to come on at 5am and turn off at 10pm.

Edited August 30, 2023 by vagrantly3893

[JohnMo]

Sounds like you have half the WC system installed. So next question does your system have 2x 2 port valves or a 3 port valve - these will be near the cylinder or boiler.