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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Hot and Cold water in boiler
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? |
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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. |
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In an earlier contribution to this discussion,
kmillar wrote: 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? I think there'd be even more unhappy combi owners than there are already if they couldn't cope with that! -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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Cheers everyone, thanks for the replies.
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kmillar wrote:
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? 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. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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"John Rumm" wrote in message ... kmillar wrote: 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? Many combis have a separate heat exchanger for the hot water side anyway. 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 http://www.usenetzone.com to open account |
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IMM wrote:
Many combis have a separate heat exchanger for the hot water side anyway. 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. Tis why I say "many" and not "all".... -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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kmillar wrote: Are boilers designed to cope with this or is there a possibility of cracking the heat exchanger? 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. |
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"Aidan" wrote in message oups.com... kmillar wrote: Are boilers designed to cope with this or is there a possibility of cracking the heat exchanger? It happens with commercial boilers, probably cast iron ones. It's called thermal shock. That is why they have back end protection, amongst others. _________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download http://www.usenetzone.com to open account |
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"Aidan" wrote in message oups.com... kmillar wrote: Are boilers designed to cope with this or is there a possibility of cracking the heat exchanger? It happens with commercial boilers, probably cast iron ones. It's called thermal shock. That is why they have back end protection, amongst others. _________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download http://www.usenetzone.com to open account |
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IMM wrote: That is why they have back end protection, amongst others. 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. |
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"Aidan" wrote in message ups.com... IMM wrote: That is why they have back end protection, amongst others. Nope. Yep. 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. 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 http://www.usenetzone.com to open account |
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IMM wrote: to close the valve so water from the flow mixes with the cold slug to keep the temp above 60C. 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 Tr60 degC, which might not prevent thermal shock. Back end protection is nothing to do with thermal shock. |
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