Summary bar graphs missing on a few days?

Emoncms Emoncms.org
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Hi folks

I’ve been uploading my gas boiler data from Home Assistant for a while and I can see all of the data arriving in Emoncms - app view . However, on a few days I’m missing the summary bar graph. e.g. below. What is causing the gaps? I’ve checked and can’t see any missing info on the uploaded data graphs. Any advice would be very welcome. Cheers.

Tim R

Screenshot 2025-10-21 at 11.52.05
Screenshot 2025-10-21 at 11.52.052264×1408 269 KB

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Hello @gr0mit I’ve just fixed the energy feeds for you, they needed recording using “log to feed (join)”, this joins across small gaps in the data. The missing bars result from null values in the kWh data at midnight, log to feed join removes these

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Hi Trystan - Amazing! Thanks so much. How does my gas boiler performance compare with others? I am currently running it with a home-built weather compensation curve controlled by Home Assistant. Found a way to programatically set the flow temp of my Vaillant system boiler, and I’ve also reconfigured to PDHW (you can see the higher temp setting when CH is not called for, where DHW heating the tank.

Cheers

Tim

1 Like
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Hello @gr0mit Im sure you are already aware of @tomasmcguinness’s monitored gas boiler? My gas boiler data is live!

Looks like yours is working well!

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There’s also @critictidier @showpiece.bsky.social on Bluesky and Emoncms - app view

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I can see a lot of misfires which isn’t great. If your boiler supports OpenTherm then you might benefit from GitHub - Alexwijn/SAT: The Smart Autotune Thermostat (SAT) is a custom component for Home Assistant that works with many compatible gateways for your boiler. @gr0mit

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Hi - Thanks for your observations. Can you explain what you mean by misfires?

Just FYI my control system is using ebusd and Home Assistant to set the flow temp of the CH water to match a heat curve that I’ve implemented based on external temperature and required internal setpoint of 21 Celsius. The heat curve is based on Michael dePodesta’s Vaillant Ecotherm equation.

I looked a while back at buying the Dutch Vaillant Opentherm board but it was nearly €200 after import duties (stupid stupid Brexit) so I opted for the ebusd interface instead, and implemented everything in HA. Because why not re-invent it?!

Cheers

Tim

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Also, part of the problem is that the boiler, a Vaillant 24kW beast of a thing, doesn’t modulate down low enough, so it’s always cycling. Any way around this?

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What’s your boiler model?

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Hi

It’s a Vaillant Ecotec Plus 624

GC No. 41-044-47

Was installed in 2011.

Cheers

Tim

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Misfires are when boiler starts but then immediately ends the cycle < 1min.

It seems that your boiler modulates down to about 8kW, not great but with low load compensation it would help for sure.

I can’t advise and promise anything but I guess you would need this module

https://www.vanwalraven.com/en/artnr/336472/vaillant-opentherm-modul-vr33

And then you’d need to buy the OpenTherm gateway from the Nodo Shop

For information about what low load is

Low load - in simple terms - max cycles per hour (3 or 4 for a boiler) where the duration of each cycle is calculated and controlled with precision (like PWM). Uncontrolled / normal cycling is when they are not restricted on how many per hour and duration is not precisely controlled.

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I have a Glowworm Ultracom 18hxi (was 30hxi). This is basically the same boiler as your Ecotec, both based on a Saunier-Duval design, and had much the same problems as you. I also have it under eBUS control. It has some “interesting” features

  • It has a very aggressive over temperature trip. If the flow exceeds the flow set point by a couple of degrees, then it shuts down until it is happy everything has settled down. It wouldn’t be so bad if this was only active on the maximum flow temperature, but it is active on the current flow set point, and is exacerbated by the next point ……
  • It always starts up at full bore, so if the flow set point is anywhere near the current flow temperature it will overshoot and the over temperature trip mentioned above activates and it stays in this cycling hell for hours.

There are a few things you can do

  • You can range rate it if you don’t need the full 24kW. In the installer menu the first option (d.0 I seem to remember) allows you to limit the maximum output to any value down to its’ minimum modulation (8kW-ish). This means it is less likely to go unstable on part loads. It also means that the house will take longer to warm up. A side benefit of this is it will reduce any ticking pipe noises on start from cold.
  • Divide the control algorithm into 2 distinct strategies ………..
  • When the house load is sufficiently high that the boiler can modulate smoothly then just use your weather compensated flow set point as you are now.
  • When the house load is not sufficiently high then alternate between max flow temperature and boiler off, but using your weather compensated temperature as a simple ON/OFF control (like the simple old bi-metallic room thermostats). Also enforce a boiler minimum on time, I use 5 minutes. I tried more complicated energy integral control for this, but the simple thermostat is good enough to not warrant the extra complexity. You should be able to do that with HA.

My boiler graphs are here

You will see periods where it is modulating fine, and other periods where it is cycling, but in a controlled manner. It is in tandem with a heatpump, hence the apparently “odd” behaviour (the HEMS decides which to use based on current fuel cost)