Bi thermal heat exchangers ?

[gassafe]

Bi thermal heat exchangers... I think there called that anyway... The ones in old Worcesters 24i, and combis with no plate heat exchanger & diverter valve.

I have to look at one next week. Customer says water flow poor, hot water almost boiling at taps!!

Sounds like the heat ex is scaled up, but I can't get my head around the design of this heat exchanger! Surely in the winter with central heating on, the water side of the heat exchanger would get super hot, boiling almost whilst water not being drawn off...? This would also explain scale build up as its going above 65 calcium type deposit temps? Is this the reason there not used anymore?

 

[lame plumber]

check the mains stopcock is fully open before doing anything with the boiler!

 

[gassafe]

check the mains stopcock is fully open before doing anything with the boiler!

I think cold water pressure is good, so sounds like boiler related... But shall check anyway

 

[lame plumber]

Bi thermal heat exchangers... I think there called that anyway... The ones in old Worcesters 24i, and combis with no plate heat exchanger & diverter valve.

I have to look at one next week. Customer says water flow poor, hot water almost boiling at taps!!

Sounds like the heat ex is scaled up, but I can't get my head around the design of this heat exchanger! Surely in the winter with central heating on, the water side of the heat exchanger would get super hot, boiling almost whilst water not being drawn off...? This would also explain scale build up as its going above 65 calcium type deposit temps? Is this the reason there not used anymore?

seems to work ok in intergas boilers

 

[GrahamM]

Who says these type of combined heat exchangers are not used any more?
Quite a few recent combis without a separate plate heat exchanger. Modena HE off top of head.
I think a lot of manufacturers went down this route of plate heat exchangers due to scaling up and being easier/cheaper to replace the plate itself.

If its the old 24i check you have decent cold supply and then the filter on cold water inlet. If that ok the heat exchanger probably scaled up.

 

[arran197]

They're called twin pass heat exchangers, the pump doesn't run so the ch doesn't come on when the dhw is being used. They may run briefly if there is prolonged dhw use. They stopped using them for several reasons, the heat loss through heating up the ch water when not used, the heat ex cost if needed to be replaced, the scaling up of heating the water directly.

 

[diamondgas]

Bi thermal heat exchangers... I think there called that anyway... The ones in old Worcesters 24i, and combis with no plate heat exchanger & diverter valve.

I have to look at one next week. Customer says water flow poor, hot water almost boiling at taps!!

Go with a thermometer and 'flow cup'! Cold water supply temp has risen quite a bit recently... ! The design has been around ages to be honest... 1st I remember was a Saunia Duval 920 thereabouts? If the complaint is water too hot then check out water flow rate against expectations IMHO

 

[gassafe]

Went there today, cold water was 16 lpm, hot water was 5 lpm!

I descaler attached descale machine for about 1 1/2 hr, re connected, and only got 6 lpm!! Ahh!

Filter on cold inlet clear, so took out flow switch and it had the most stupid restrictor in there! Hot water flow now okay!! I shall always check those first now!!