If my boiler is running, and servicing the central heating, then after some time the Hot Water is demanded, won't a flush of cold water end up going through a very hot boiler? (From the HW Flow via common return).
Are boilers designed to cope with this or is there a possibility of cracking the heat exchanger?
They are designed to cope with this.
Christian.
I think there'd be even more unhappy combi owners than there are already if they couldn't cope with that!
Cheers everyone, thanks for the replies.
Many combis have a separate heat exchanger for the hot water side anyway. What happens if the burner heats the main exchanger as usual, a diverter valve switches the the flow of heated water from round the radiator circuit to a small circuit that just includes the secondary heat exchanger, this then transfers heat to the mains cold water.
I few don't and the main gas heat exchanger has cold fresh water running through it. It is designed to cop with excessive low temperatures.
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
It happens with commercial boilers, probably cast iron ones. It's called thermal shock.
I've never heard it mentioned with regard to domestic boilers, if it was a problem, there'd be big warranty claims. I think the answer is no in that context.
That is why they have back end protection, amongst others.
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
That is why they have back end protection, amongst others.
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
Nope. Back-end protection is intended to protect against back-end corrosion, i.e., prolonged cold start return condensing temperatures of less than
60 degC. It wouldn't necessarily protect from excess dT/ thermal shock caused by a slug of cold water from switching on a dormant zone, although it may help. Protection against the possibility thermal shock should be incorporated in other design details. Finish.
Yep.
Having the back end protection sensor on the return would keep the water temp into the boilers return higher than say 60C (condensation does not occur above this). When a remote wing of the system is switched on. A slug of water at say 10 C may be pumped into the boilers return, the sensor immediately sees this as the return water temp drops below 60C and immediately starts to close the valve so water from the flow mixes with the cold slug to keep the temp above 60C.
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
Close the valve?
If it is a valve, it's generally a 3-port diverting valve, which doesn't close, it diverts. Also, could be a shunt pump. Both are intended to stop back-end corrosion, not thermal shock. Both stop working when Tr>60 degC, which might not prevent thermal shock. Back end protection is nothing to do with thermal shock.
Of course it is'nt, it is a 3-way "mixing" valve. It is clear you only have half a clue how it works.
But the 3-way "mixing" valve keeps the temp above 60C into the boilers return.
You can do "both" with a good controller, quick action sensor on the boilers return, and a 3-way "mixing" valve. It used to design them.
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
Tis why I say "many" and not "all"....
Could be either, a 3-port mixing valve or a 3-port rotary-shoe diverting valve. Either way, it's still a 3-port valve and it doesn't "close", as you had stated. You've obviously been Googling to try to find out something about this. You're just digging yourself in deeper.
You've misunderstood that; whichever website you've got that from probably mentioned quick action re the actuator.
You are a trolling idiot!! It is quite clear I know exactly what I am on about. It is clear you only have half a clue, if that. Read what I wrote. It is good for you, as you now know something new.
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
Hello pot meet kettle....
ROTFLMAO... go on tell us another, I could use another good laugh.
What a stupid thing to say.
Wow is this good old Yorkshire humour? By gum. Fraid it goes over all humanities heads, that one.
Do you talk to dolls as well?
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
par for the course then...
Other than you? No.
You are that way inclined? Inverted? Boy!
_________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.