Hot water too hot

[ma701ss]

Hi, I asked this some time ago but never got to the bottom of it. Is it normal for a combi to give out hot water that is much hotter than the temp set on the boiler and then reduce down? It starts off cold for a few secs, rises to about 60 degrees quickly and then levels out to the correct setting of 45 after about 10 secs.

 

[Last Plumber]

Which Boiler is it ?
Make, Model Size ( output ) ?

 

[ma701ss]

Ideal Logic + C35
But I wondered if it is the general behaviour of combi's?

 

[Masood]

Have you got thermostatic mixer taps? Starting off cold is normal - there will be an amount of water in the pipework that needs to be run off before the hot comes through.

 

[ma701ss]

Yes I realise starting off cold is normal, it's the getting hotter (too hot) and then reducing to a cooler temp that seems odd. TMV's are not fitted but that seems to be the only way to stop it scalding. I'd presumed that if I set the boiler to 45 degrees it would only ever get to that or cooler.

 

[Masood]

Yes I realise starting off cold is normal, it;s the getting hotter (too hot) and then reducing to a cooler temp that seems odd. TMV's are not fitted but that seems to be the only way to stop it scalding. I'd presumed that if I set the boiler to 45 degrees it would only ever get to that or cooler.

TMVs are not the same as thermostatic taps! Do you have thermostatic taps? The boiler will have sensors controlling the hot water temperature but like all sensors they have a reaction time. The heat exchanger will retain heat for a while after the sensor has sent a signal to the boiler to modulate down, so it is feasible that you'll get a slug of hotter water as well. But thermostatic cartridges have a relatively short lifespan in my experience, especially the cheaper ones.

 

[SimonG]

All depends on the flow.

 

[Geyser]

Well it's an Ideal Logic so you get what you pay for. But that aside there is always a delay from heat generated to the thermistors sensing it and modulating the temp and variable flow rate through hx .

 

[ma701ss]

Hey, my Ideal Logic plus boiler is the nuts
No to thermostatic taps but don't they work the same way, by mixing hot cold to achieve whatever temp it's set to?

 

[ma701ss]

All depends on the flow.

What do you mean by depends on the flow? I'm, assuming that if a boiler is set to 45 degrees it should never heat water above that temp, how does the flow affect it?