Bosch easycontrol ct200 smart thermostat advice please

[fitzykev]

..and did it fully heat the radiators, to a hot temperature?

You need to put your heating system through some stress, to ensure it is working as it should first, before worrying about the controls.

Ai explanation
If the boiler is still burning gas even after the room has surpassed your "Optimum" target temperature, it usually comes down to how the CT200 handles Modulation versus a simple "Off" command.


Here are the three specific reasons why it’s still firing:

1. The "Approaching Target" Logic (PID Control)​

The CT200 doesn't just cut the power at 20^\circ\text{C} if that's your target. It uses an algorithm to decide how much power is needed to maintain that heat.

• The Glitch: Because it’s new, it thinks it needs a "high fire" to reach the target.
• The Result: Even when it hits the target, the software might still be requesting a low level of heat from the boiler to "stabilize" the temperature, mistakenly thinking the room is still losing heat rapidly.

2. Maintenance Cycles (Calibration)​

In the first 48 hours, the thermostat often runs the boiler longer than necessary to measure the "Upper Thermal Limit" of the room. It needs to see exactly how high the temperature climbs for a specific amount of gas burned. It "over-fires" once or twice so it can mathematically "map" your home's insulation levels. Once it has that data point, it will start cutting the gas before it hits the target next time.

3. Flow Temperature & Weather Compensation​

If your CT200 is using Weather Compensation (either via an outside sensor or internet data), it might be telling the boiler: "It’s cold outside, keep the water in the radiators at 65°C."

• If the room is already at your target but the "Flow Temperature" hasn't been reached yet, the boiler will keep burning gas to heat the water inside the pipes, even if the air in the room is already warm enough.

How to stop the "Runaway" Heat:​

1. Check the "Influence of Room Temperature" setting: In the app (Settings > Heating > Control Strategy), ensure this is set to High. If it's set to "Low" or "None," the thermostat cares more about the outside weather than the actual temperature in your lounge, which causes it to keep burning gas indefinitely.
2. Verify the "Maximum Flow Temperature": If this is set too high (e.g., 80^\circ\text{C}), the boiler will work much harder and longer than a smart thermostat needs it to. Reducing this to 60^\circ\text{C}–65^\circ\text{C} often stops the overshoot.

Is your boiler a Bosch Greenstar or a different brand? Knowing the brand helps determine if the thermostat is communicating via "OpenTherm" or just a basic "On/Off" signal.

 

[fitzykev]

So i spoke to worchester bosch and they reckon to just leave weather compansate off. They reckon because its not to cold out and i have it turned on it is telling itself to burn low. Kinda defeats the purpose if you ask me tho. You would think it should know to burn a little bit warmer.

 

[izaimza]

Bosch are probably right here — in mild weather the CT200 can undercook the system if weather compensation is active but the curve/settings aren’t really tuned yet.
Before blaming the stat itself, I’d do 3 quick checks:

1. turn weather compensation off for 24–48 hours,
2. set a fixed flow temp around 60–65C and see if it actually reaches target on schedule,
3. turn the room target right up once and confirm all radiators get properly hot and the TRVs aren’t throttling things.

If it behaves normally with fixed flow / weather comp off, then the boiler and controls are basically fine — it’s the compensation setup, not a faulty thermostat. If it still crawls, I’d be looking at balancing / pump speed / control wiring next.
Not Bosch-specific, but this plain-English UK guide on smart thermostat behaviour / options is useful as background: https://www.smarthomeuk.co.uk/best-smart-thermostats-uk-2026-complete-buying-guide/

 

[fitzykev]

Bosch are probably right here — in mild weather the CT200 can undercook the system if weather compensation is active but the curve/settings aren’t really tuned yet.
Before blaming the stat itself, I’d do 3 quick checks:

1. turn weather compensation off for 24–48 hours,
2. set a fixed flow temp around 60–65C and see if it actually reaches target on schedule,
3. turn the room target right up once and confirm all radiators get properly hot and the TRVs aren’t throttling things.

If it behaves normally with fixed flow / weather comp off, then the boiler and controls are basically fine — it’s the compensation setup, not a faulty thermostat. If it still crawls, I’d be looking at balancing / pump speed / control wiring next.
Not Bosch-specific, but this plain-English UK guide on smart thermostat behaviour / options is useful as background: https://www.smarthomeuk.co.uk/best-smart-thermostats-uk-2026-complete-buying-guide/

I got it running correctly. Turned the boiler up to 75 but set my heat curve to 65 so although boiler is at 75 the heat curve does the work