What happens when last valve closes at the end of heating cycle?

fus

Hi!

Setup: all radiators with tado thermostatic valve + thermostat to control the heating start/stop

Scenario: heating is on, last thermostatic valve reaches set temp and closes → thermostat should switch the heating off

Heater PoV: 'stop' signalled from thermostat so burner goes off, and the water pump kept on until the residual heat in the medium is circulated out

Question: is Tado system taking into account that there is still heat to be circulated out, and that keeping all thermostatic valves closed makes the pump run without flow over some period of time? If yes, then how is it handled? And if not, then when will it be handled and how? :)

Thanks, Tomek

eezytiger

Common wisdom is to leave one radiator without a TRV, so that it is always open for the pump to run on. This is known as a bypass radiator.

I don't believe that Tado logic keeps valves open just to accommodate pump overrun. Indeed, historic experience has shown that Tado might call for heat from a radiator and yet fail to open the valve sufficiently for water to flow. That's another very good reason to keep an open radiator in the loop.

I actually have two such radiators in my home. One is without an SRT. The other is responsible for firing the boiler and I've fitted the SRT loosely, so that it can monitor temps and request heat, but can never close off the radiator.

EDIT : Just to add - some boilers have a built in bypass loop, so a bypass radiator is not strictly necessary if the boiler has this feature.

samd

@Tomek Do you have a bypass? If not standard practice is that you should keep one rad permanently open (does not need tado TRV)

fus

hey, thanks for quick replies!

I don't have smart thermo stuff installed yet - that is a theoretical situation.

I am well aware that "you don't install thermostatic valves where your room thermostat is" and I fully understand why. I was just trying to find the level of "smart" in Tado ;)

Coldest room/rad gets "loose" Tado valve then!

eezytiger

Yes - it is my coldest room that has the loose valve. This room is also responsible for requesting the boiler to fire. All others are set to "independent".

samd

@fus Agree with everything that @eezytiger has said but note that his comments were on the basis of 'whole house' heating. Taking note of how you 'operate' on a daily basis AND the efficacy of your insulation, it may be preferable to use the facility to turn on/off individual rooms as and when required.

Irek85

Safety measures are always good to have - as @eezytiger stated.
I had a problem with valves closed and boiler heating, but Tado support managed to implement some fix that made it stop. I've heard that some users corrected (with the help of support) how much their radiators valves open as minimum - to mitigate risk of valves not sufficiently open to dissipate heat.
Based on that I think it's possible (with help of someone willing on Tado side) to set up the system the way you want. However - if I've known before how hard it's to get real help from support - I probably would look elsewhere.

fus

@samd, yes, you are right that a 'loose valve' wouldn't work perfectly for 'heat on demand' for any of the rooms.

In my opinion the best solution would be to just keep the last open valve open in a 'bypass' mode, when it reaches set temp.

Then the signal to start heating from any of the valves should just reset this 'bypass' mode and thus make the system enter standard heating mode.

This could be done with an update to the app (and/or valve firmware) but would need to rely on the valves operating as they are expected, so there would still be risk that a valve fails to open (either due to software or a mechanical issue), like mentioned by @eezytiger.

So for now I understand that if there is no dedicated bypass loop at the boiler, there must be (for safety reasons) one radiator always kept open (also even with a boiler bypass loop when boiler is in the cellar it may actually be a better idea to dissipate the remaining heat into the living space)