My gas boiler data is live!

With some help from Glyn and Trystan, my gas boiler is now being monitored and logged to!

You can view the data at

Interesting to see my boiler’s efficiency is hovering around 92% over the last few days which is great! It would be great to see it hit 94/95 which is the theoretical max for a return temp around 35.

As always, I’ve made a video documenting the setup.

Happy to dive into more details if anyone is interested!


Nice work putting this video together @tomasmcguinness it’s a great overview of the steps involved getting the data into emoncms from home assistant.

For anyone else interested in the boiler monitoring app, this is was a relatively simple copy of the myheatpump app but with the heat pump bits stripped out and an extra feed for gas input among a few other UI changes. The app is available in the latest version of the emoncms Apps module. Source code available here (within the wider app module):


Interesting looks like the delayed gas reading created a glitch for yesterdays total, suggesting an efficiency of 99% ! today is lower but you’re also running the higher flow temp test I guess. Perhaps the gas input energy needs to be displayed as a step plot on the graph so that you can select a window that includes the delayed gas reads…

Could this be caused by the call for heat flag being incorrect?

I changed the wiring to my Shelly i3 at lunch time today, so the call for heat should be accurate going forward.

@Zapaman suggested a pulse counter approach - I need to investigate this as it might provide faster updates.

I think it’s just window alignment with when the kWh values are incrementing…

I’ve made a minor change to show the efficiency in the window and fuel kWh values stepping up, it’s now much easier to manually select to get the right alignment:

It’s not showing much of an efficiency loss though with 50C vs 43C… maybe it’s not enough of a difference… ? interesting stuff!

The return temperature is too low to make any impact at this stage. I suspect once I pass a 60 flow temp…

Maybe I should just do a week at 60 and a week at 70?

Sounds good! what’s the max temp you can run it?

Chatting to Glyn here, it might be that it will be difficult to assess the impact during these milder conditions as run times are not long enough to get the average return temp up?

E.g average return temp when running here was 34.6C, it rises and levels off at 38C…

Is there a digital version of that boiler efficiency chart where you can dial in the return temp and it spits out the expected efficiency?

If you can find a good algorithmic fit I can try and add it to the boiler app as an efficiency simulator :slight_smile:

One of your best runs so far:

  • 93.8% including electric
  • 96.2% fuel to heat only (not including the 0.359 kWh of electric)
  • return temp average when running: 34.4C

The fuel to heat only in that example is spot on the chart!

Perhaps the efficiency should be reported as two separate figures one with and one without the electric…

As I read that, I’m reminded that boilers will try and maintain a 20 dT (somebody on this forum actually told me that)…

Perhaps I should just jump to a 65 flow, which should see the dT rise to 45, based on that assertion?

I suspect that efficient chart doesn’t take electricity into account!

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DT20 probably just a rule of thumb similar to heatpumps need DT5 I guess…

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They implied that the boiler’s pump would strive for 20dT, which would explain why rising the flow to 50 didn’t impact the return temperature?

Higher flow temp results in hotter radiators and more heat output which will give higher DT if flow rate has not increased…

Yeah. The flow rate doesn’t appear to have changed at all.

My radiator sensors aren’t quite setup. Battery died in one I think, so the mesh has failed :joy:

These show the return temps are north of 40 on the rads that are communicating. The lack of balance is probably having an impact.

I’ll ramp the boiler up to 55 in the morning all the same :slight_smile:

I configured the My Boiler app (directly on here

Set up in the same way as Heat Pump App, Inputs and Feeds showing live values, but the My Boiler App configuration page does not display a “Launch App” button in the same way as the Heat Pump App does. Not sure what I have done wrong.

Ok, figured it out. It seems to require the boiler_elec feeds to be populated. Since this data may not be easily available, seems better to make those fields optional?

It needed the boiler electric consumption data (pump, boiler fan etc), I’ve removed that requirement now. Looks like your getting about 80% from this one so far?

Yes, when not condensing it seems to manage 80%-ish, once it has settled down and is condensing it gets into the 90s. Be interesting to see how it measures up, it is best part of 16 years old. part of a hybrid set up with a Heat Pump.

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Thanks @toadhall interesting comparing with:

between both of your boilers you have most of the range it seems (other than the few below 80%)

Hey @toadhall, how are you getting such granular fuel data?