TL;DR: How do I make the thermostat send a ‘heat’ request to the boiler without making the boiler use way too much gas?
Hi all,
I have a question about automating central heating. My current setup:
Ground floor:
- Main thermostat linked to boiler (Honeywell T6 on WiFi through Honeywell integration)
- One radiator with Sonoff TRV-ZB, zigbee
- Three radiators with non-smart knobs that are usually open
- The main room has a Sonoff Presence sensor
First floor:
- Three rooms that can be occupied with Sonoff TRV-ZBs.
- Two of three rooms have Sonoff Presence sensors
All rooms that can be heated smartly are controlled through a blueprint once shared here called ‘Advanced heating control V5’.
I have a helper called ‘Comfort Temp’ which is a slider that controls the setpoint on the main thermostat and the TRV of an occupied room.
So the obvious question is: is there any good way to get the main thermostat to send a heating request to the boiler?
I’ve seen something about a WiFi module that you can put in between the main thermostat and the boiler that offers more control (Nodo OpenTherm Gateway, OTGW). Does anyone have experience with this? Or do I solve this with more TRVs on my ground floor? I’ve heard about central heating systems not enjoying a fully thermostatic valved circuit. More TRVs also means I have to replace the valves on a couple of radiators.
Any advice would be greatly appreciated!
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Just to make sure: You have zero buffer tank between your pipes and the boiler?
Just chiming in to say I think this guy’s got the right idea. I realize what community this is posted in, but sometimes when you’re really into your hammer everything starts to look a little too much like a nail. If you have room for it (sounds like a pretty big house) a buffer tank would make a huge difference
‘Big’ is relative. It’s a house in between two left and one right in a block of four. It’s big enough for two people, but it’s not huge.
I’m not sure I understand the function of the buffer mentioned. Is it a heated buffer that can pump around hot water without having to expend gas to heat? How does that differ from the expansion vat I have? Is that just to soak up excess pressure?
Sorry about all the questions, I’m just not sure about all of this stuff.
In most hydronic heating systems I’ve worked on, there’s an insulated tank of hot water either somewhere in between the boiler and radiators or built into the boiler directly. The thermostats talk to valves that send the water to radiators in the rooms that need it. The boiler just keeps that water at a set temperature.
In larger buildings with really long runs, sometimes there are valves to bypass certain radiators and/or multiple tanks located around the building. I can’t say without more information about your home, but it might make sense to have one near the area you’re trying to heat most.
No storage tank at all and thermostats that fire up your boiler directly sounds very unusual and inefficient. The expansion tank you have is just meant to stabilize pressure, it doesn’t have enough volume to do much for temperature
Ah no there is one of those expansion vats in between. It’s not huge but it doesn’t need to be.
Okay. Shame. Because basically that’s what would help you most.
English is not my first language and although I can kinda get my point across, technical jargon is a bit of a blind spot. So just to clarify: I have a little vat of say 10 liters connected to the heating pipes. It’s next to the boiler. It contains a rubber membrane in the middle to expand if pressure builds. Is this the type of buffer you’re referring to?
No worries. And while English is not my first language either,I think you were right with the term expansion tank - these are sadly only meant for keeping the pressure stable, not really “buffering”.
A buffer tank is large (often 500+x l) and well isolated. A bit more modern heating systems use them to, well, basically buffer things- the water in it is heated up (with the actual heating system running under ideal operational parameters and while it takes long its needed less frequently) and then the house getting its heating demand out of that. This is basically the ideal solution for your issue.
But sadly its often not feasible installation wise - while they are not that expensive they need a lot of room, a floor that can actually bear the weight and of course someone who install them.
But maybs speak to a professional about it if you own the place - it might be cheaper in the long run if you combine the costs of the alternatives, and these days they have creative solutions sometimes.
I’m really confused by your post. The questions don’t seem to match eachother’s. I feel you have not made clear the specific use case you’re troubleshooting.
I am an inexperienced knob on Homeassistant and home automation, that lurks here out of curiosity and to catch some easy crumbs left around.
But, I feel that I know enough about central heating, radiators and thermostats to justify commenting.
The central heating boilers, pretty much always, just work as on-off. With some internal (boiler) logic on safety limits, like the working temp of the radiator fluid.
Thus your obvious question has an obvious answer. The way to have the main thermostat sending a heating request is to lower it’s setpoint temp.
At the same time, the TRVs are supposed to limit/moderate the lowness of the main thermostat setpoint, i.e., to moderate the way in which the main thermostat activates the boiler ‘too soon’. And TRVs allow you to adjust the comfort of each room (as long as the main thermostat is already requiring the boiler to be on).
As for the presence sensors. Radiators take a long time to heat a room. Like dozens of minutes. If the presence sensors work as their name suggests, I feel they are not a good match with radiators. Plz teach me!! How do these work? What happens when you are sleeping, or when siting, reading, or watching TV, or in the computer.
“I’ve heard about central heating systems not enjoying a fully thermostatic valved circuit.”
‘Enjoy’? Ehh, the pump (usually a part of the boiler) and the tubing that make the radiator’s fluid circulate, from the boiler around the house and around the radiators, they are not contructed/designed to have the circuit closed. 100% closed. Thus the recomendation not to put TRVs in all radiators - which could potentially all close off at the same time and damage the circuit (with overpressure). The recommendation is to have at least one radiator with it’s manual valve always open. The recommendation is also improved to have this radiator in the bottom of the house or the closest to the boiler, instead of a radiator in the top floor bathroom where you’ve left open the window to let out the moisture or something.
Again, what is it really what you want to solve?
The issue I’m trying to solve is to heat a room upstairs whilst not having the boiler in a constant ‘on’ state (the main thermostat is modulating and uses OpenTherm to communicate but that’s beside the point).
A use case: say I’m going to work in my room upstairs. It’s currently 18°C. The living room, where my main thermostat is, is 18°C. I have my coffee in the living room, causing my automation to recognize I’m in the living room.
I move up to my room and set my comfort temp to 20°C. The thermostat in the living room adapts to that. So does the TRV in my office. Since the setpoint of the main is higher than the measured room temp, it sends a heating request to the boiler. One of the radiators in the living room is closed, since the presence detector don’t show occupation in the living room.
In this case, my office might not make it to 20°C before the living room does. The pump stops and no newly hot water gets sent to my office even though the valve is open.
Bottom line: with the current blueprint I mentioned, everything works moderately well. What I want to avoid is to have the boiler heating water if the only occupied room is already at its setpoint. What I want to achieve is more control over when the boiler should heat water (and also pump it around) so that I don’t have to heat the living room when heating, say, the bedroom.
Oh and as far as the time between presence sensing and heating goes: I’m fine being a little chilly for ten minutes. Like I said, I keep every room at a minimum of 18°C to make sure it never takes too long to heat if I want it.
Having seen this webpage https://www.draytoncontrols.co.uk/news/opentherm-explained , which kind of modulation do you have? Long boiler runs are not always bad.
Also, are you able to use the living room TRVs to restrict the livingroom radiators heat output while keeping what you have set as the main setpoint, in the use case you detailed. That would avoid having the main thermostat triggered off too soon.
There is only one TRV in the living room because the other valves are not thermostatic. I would need to replace those to achieve what you describe. But then I think that’s not the way to go because it could damage the pump from what I hear.
The boiler is a Remeha Tzerra Ace which supports Opentherm with modulation. It’s also wired on the opentherm contacts and the T6 supports it.
I use the Hive integration and just let the Hive stuff do its work, monitoring via Home Assistant occasionally. My setup is the Hive thermostat, boiler relay and the hub
I went down a rabbit hole of TRVs, automations, Shelly relays talking to the boiler, zigbee thermometers everywhere, and it got complicated. Ultimately the big risk was the system getting stuck or in a state where the boiler would be on all the time and cost a fortune, so I got rid of it all.
If Hive no longer meets my needs I know I can just pair the hardware to my zigbee network and stop using the cloud service.
I use Honeywell Evohome which controls both the rooms via TRV and the boiler via standard thermostat control. Either on/off in the case of no open therm or on off and temperature modulation in the case of open therm (which I upgraded my boiler to when it broke). It works very well and has good homeassistant integration including a local one.
I considered this when getting my TRVs but I prefer it to be Zigbee. Also I’m not planning to substitute all my current TRVs for different ones, that’ll be a costly operation. I think if I was looking for a closed (ie one manufacturer) system I might lean towards Tado or maybe PlugWise.
Thanks for the suggestion!
Tado does temperature modulation through OpenTherm or manufacturer specific EMS. In the UK the older V3 models didn’t support it though (for reasons I didn’t fully comprehend, ended up getting an Extension Kit off eBay which does support it), I think Tado X is less of a minefield in that department.
