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Phil, Mechanical Engineer.
Category: Plumbing
Satisfied Customers: 8768
Experience:  Retired mech. contractor, shop owner, 51 yrs experience.
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Rick I have an issue with the hot water on the ethos 54c it

Customer Question

Hi Rick
I have an issue with the hot water on the ethos 54c it works for 5 min and boiler switches off completely.
I ll have to wait for few min to restart
Replace hot water heat exchanger and diverter but problem still there.
Can u advise any further ???
Submitted: 1 year ago.
Category: Plumbing
Expert:  Phil replied 1 year ago.

Hello Peter, does this look like the manual for your boiler

click here please

Tell me please about how old it is, and if you have ever acid cleaned its heat exchanger or not. (I suspect that it is tripping its high limit due to water scale in the heat exchanger).

Customer: replied 1 year ago.
Hi PhilThe boiler is about 8years old the heat exchanger and diverter have been replaced recently.Look forward to hearing from uThanks
Expert:  Phil replied 1 year ago.


Try locating the high temperature safety cut out switch, then follow its two wires back to printed circuit card, then fit a jumper across the two wires using wire nuts.

The high limit switch is shown on the wiring diagram and is mounted on the primary heat exchanger.

Customer: replied 1 year ago.
Will do that tomorrow and get back to u
Expert:  Phil replied 1 year ago.

That will work.

Customer: replied 1 year ago.
Hi PhilI went today and have linked the wires to the high limit stat but made no difference.
Also I found out that the digits to the PCB are stuck when I tried to reset the boiler.
On the heating boiler works fine.
Do u recon is the PCB ???Give me ur advice.Regards
Expert:  Phil replied 1 year ago.

Thanks Peter, restore the wiring to the high limit switch exactly as it was before, then set it down as low as it will go as a TEST...

the boiler should not attempt to fire with the high limit set below the temperature of the water in the boiler.....

then set the high limit switch to 175F and the boiler should fire. That is a critical test of your boilers high limit safety switch. We need to make 100% sure that it is wired correctly and functioning.


Do this heat stress test on the printed circuit board

Use a hair drier to slowly warm the printed circuit card up to120F or a bit warmer, but not over 140F... if there is any change in the error codes or other furnace behavior... the card has a cracked micro circuit that opens and closes as the card expands and contracts... that proves a bad printed circuit card.

No change however does not prove the card is good however... but a change proves the card is definitely bad.


When you refer to 'digits on the PCB' do you mean the tiny white dip switches? If so, they do not stick, but they can be stiff at times the appearance of being stuck would not indicate a bad PCB.

None the less, PCB failure is common. Use a magnifying glass and look for burnt or corroded or copper oxide spots (green corrosion) on the PCB.. if you see any of that, the board is quite possibly bad.

If you can use the paper clip icon at the right end of the tool bar, or the attach files link to the left of your send button to send me a close up of the 'stuck digits' I can be more explicit.

also, let me know how the heat stress test goes.