Hansen hot water overflow on mains

Submitted: Saturday, Jan 02, 2016 at 14:18
ThreadID: 131251 Views:1150 Replies:3 FollowUps:1
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Can anybody help me we have a Hansen hot water unit which I have only ever ran on tank pump have plumbed in Mains and it pushes water out the hws overflow even with the mains turned down at half pressure of what the pump runs at can anyone help
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Reply By: The Bantam - Saturday, Jan 02, 2016 at 18:12

Saturday, Jan 02, 2016 at 18:12
I don't know you exact HWS ...... BUT .... pretty much all hot water systems that are connected to mains supply are connected thru a non-return valve ( required by law)....... also pretty much all hot water systems have some sort of pressure relief or overflow. ( required by law)

SO as a hot water system heats up the water inside expands, the overflow or the pressure relief allows the water to escape.

If that was not so ... this would happen ...

cheers
AnswerID: 594407

Follow Up By: The Bantam - Saturday, Jan 02, 2016 at 18:13

Saturday, Jan 02, 2016 at 18:13
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FollowupID: 862787

Reply By: Notso - Sunday, Jan 03, 2016 at 10:33

Sunday, Jan 03, 2016 at 10:33
" even with the mains turned down at half pressure of what the pump runs at "

How are you turning down the pressure of the mains. If you mean just turning the tap off till it is restricting the flow of water; this doesn't alter the pressure, as the pressure in the system will equalise with the pressure in the pipes as soon as you stop drawing water off.

It could well be that the pressure in the mains exceeds the blow off pressure of the relief valve. You may have a faulty or non existent pressure regulator on the mains inlet.
AnswerID: 594437

Reply By: Allan B (Member, SunCoast) - Sunday, Jan 03, 2016 at 15:15

Sunday, Jan 03, 2016 at 15:15
.
Jazmor,

According to Hansen's product specifications the water supply pressure should not exceed 1.8 bar (=180kPa or 26psi) and the relief valve setting is 3.0 bar. Mains water pressure is normally in the range of 2.0 to 4.0 bar so you would need to reduce that to 1.8 bar using a reliable pressure regulator. If this regulator is not a "relieving" type and does not shut off absolutely then the outlet pressure will creep up when no water is being consumed and exceed the hws relief valve setting.
Incidentally, be careful using Hansen's data sheets as they have confused themselves by using the unit "bar" in some places and the same values as "kPa" units in other places, but I would believe the correct values are those of "bar".
Do you have the means to measure the pressure applied to the hws with adequate accuracy?


An alternative safe method of operating the hws from a mains supply can be achieved by having a free discharge, i.e. have no tap or restriction on the outlet and control the mains water entering the hws by means of a shut-off valve (either hand or solenoid) and a flow restrictor. In this way, as the cold water is admitted to the hws it pushes the hot water out of the delivery outlet and pressure will rise very little within the hws. Hansen endorse this method.
Cheers
Allan

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AnswerID: 594449

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