What decides the hot water temp in a combi boiler?

r2015

What decides the hot water temp coming from the taps of a combi boiler?

Is it the flow rate of the water slowed down to make the water hotter or is the gas flame increased in intensity?

The same with the temperature for the radiators.

Does the water flow round faster the cooler the temperature required and slower the hotter the temperature required or is the gas flame increased or reduced in intensity?

Worcester Bosch Greenstar CDI boiler.

Alex1983

The cdi has a hot water thermostat on the front doesn’t it. If it does then it will be controlled by that but the flow rate will have a effect on it.

Ectophile

Some combi boilers have a temperature knob for the hot water, and some don't.

But even if they do, there are limits to how hot the water will get. The boiler is having to act as an instant water heater, heating up the water from whatever the cold water mains temperature is. In the summer, that's not a problem. But going into winter, the ground slowly gets cold, and so does the mains water. The end result is that the water isn't as hot as you'd like.

If the incoming water is too cold, the boiler will be running flat out trying to heat it up.

The "solution" is to reduce the flow, perhaps by partly closing a tap on the water inlet to the boiler.

Saver0811

My Combi boiler has two temperature setting knobs, one for Hot Water, one for the Central Heating Radiators.

At maximum, hot water is too hot, even with washing up gloves on, and radiators are dangerously hot with children around.

I run both at around 75%

r2015

But what do the knobs control, the flow of the gas or the flow of the water?

Alex1983

The knob is a variable resistor which works with the a thermistor inside the boiler to control the temperature of the water by adjusting the fan speed and gas rate.

daveyjp

r2015 wrote: »

But what do the knobs control, the flow of the gas or the flow of the water?

Years ago you may have had winter and summer setting knob. This was a physical connection to a part in the boiler.

Boilers are now much more sophisticated and use electronics to vary heat and water flow.

Our boiler never reaches 100% flame as its just not required to maintain even the hottest water temperature as the cold water flow and boiler size were matched properly.

Too many boilers aren’t correctly sized as the basic cold water pressure test isn’t done before selecting the boiler output.

chappers

r2015 wrote: »

But what do the knobs control, the flow of the gas or the flow of the water?

Gas burner essentially, you control the water flow rate at the taps