Can heat flow up the temperature gradient?

I am a newbie struggling to gain some understanding.

On the front of a Worcester Bosch Regular boiler there is a temperature control knob that as I understand it, controls the temperature of the water flowing out of the boiler. So if I set that to 50C, then the water coming out of the boiler will be at 50C and so on.
A technical spokesperson has just told me that if that water at 50C is directed to the primary coil of the domestic hot water cylinder, then it can heat the water in that cylinder to 60C or 70C or whatever temperature I set on the thermostat that is on the hot water cylinder.
Can he possibly be correct?
Surely, the 50C water coming from the boiler can only possibly heat the water in the tank to 50C no matter what the tank thermostat says. I agree that the boiler may go on trying - but surely it will never actually get to 60C and allow the thermostat to turn off. To do so, heat would have to flow up the temperature gradient which is surely against the laws of physics.
I will be very happy if you tell me I am wrong and that it can work the way he says, providing you explain how it happens, what it is that I have not understood.
Thankyou

No, you're right and he's wrong. Heat always flows from a hot body to a cooler body. Never the other way around.
2nd law of thermodynamics.

That coil temp control setting can be increased above the desired cylinder temp' because it is the cylinder stat that controls the cylinder volume temp, higher output (coil) temp will give a quicker cylinder satified temp.

It is a statistical certainty.
Unless Maxwell's demon has taken up residence in your boiler.

JohnArnoldBrown said:

Unless Maxwell's demon has taken up residence in your boiler.

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Not sure about Maxwell's but I can well believe there is a demon in there

Thank you all for your comments. It is a bit sad that a boiler supplier's technical helpline did not get this right. Knocks ones faith a bit.

To explain slightly, my house is well insulated and if I work through the Energy Saving Trust calculation sheet, it concludes that I only need 7kw when the radiators are all on full - an incredibly rare situation - and much less the rest of the time. Minimum gas boiler size seems to be 12kw so even that would be on tick over much of the time.

I wondered whether the boiler could be switched so that it supplied water at say 50C to the radiators when only central heating mode is called and 70C when the domestic hot water needs heating. My thought was that the boiler only condenses if the return water is below 50 and if it is set to 70C flow with only a tiny CH load, it is unlikely to be less than 50 coming back so running inefficiently. But I need 70C flow to heat the DHW to a reasonable temperature reasonably quickly.

I do not think it would be hard to organise such a switch but it is clear the boilers do not do it. I am not sure whether that is because there is a flaw in the idea or because the manufacturers cannot be bothered.

I am interested in anybody's experiences of running boilers right at the bottom of their modulation capability (and lower) and hear any ideas for keeping things efficient. Or maybe I am fretting about a non problem. What do you think

It's not possible with your boiler.

Dan_Robinson said:

It's not possible with your boiler.

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Sorry, I'm a bit dim - but what is not possible, to run it efficiently or to switch the temperatures and if you mean tempertures do you mean not possible at all even with some jiggery pokery or not possible without modification. The latter I will accept totally.

Dual flow temperatures.

It is not possible with your version of boiler.

It is possible with many others.





Well, I say impossible.... There is are ways, but not legal.

Dan_Robinson said:

It is possible with many others.

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I have not bought "my" boiler yet - can you suggest a boiler capable of dual temperatures that I can look up please?

And do you think it is a good, worthwhile idea or just unnecessary.

Intergas
Atag
Vokera

Vaillant if you are a brand follower who doesn't care about personal information going astray.