Ideal Icos m3080 blowing 3.15A PCB fuse

[mikefiore]

hi,

this is my first post here so please be gentle.

I have an 8 year old Ideal Icos m3080 which has been working absolutely fine until yesterday when it started blowing 3.15A fuses.

Prior to commencing fault finding on the boiler I verified that all the other elements in the system (controller, tank stat, room stat, three port motor valve and external pump) were functioning correctly by running the system without the boiler connected. The external pump and all ancillaries draw no more than 0.44A even with the pump on position 3 (fastest).

I have identified that the boiler unit will power up and perform a self test showing a 0 on the LED panel provided I have nothing connected to the L2 terminal (black wire) forcing a call for heat. As soon as a mains voltage is present on the L2 terminal the 3.15A fuse blows instantly.

I have checked the mains filter although if this were faulty I think the unit would not power up. I also checked internally within the PCB for signs of damage/burning and could detect none at all. I checked the operation of the control temperature sensor and flue sensor by measuring resistance and warming the devices with my fingers. In each case the temperature began to drop indicating that the sensors are functioning.

I measured the internal pump (disconnected) for resistance/short and found 8~9Mohms between live-earth and neutral-earth but saw infinite resistance from Live-Neutral (?).

So, I am pretty stumped, not to mention cold, and wonder if any of you smart guys out there have any ideas what I can do to narrow down the cause of the issue.

Thanks in advance,

Mike

 

[45yearsagasman]

Your reading of infinite or No resistance across the pump windings is a bit of a worry as is the resistance from L&N to earth.

 

[Agile]

The pump windings are going to be around 180 ohms. If yours is opencircuit then the pump is not working!

BUT what you have said is inconsistant because you had measured a pump current of 0.44 A.

So can you clarify the situation.

The boiler has a live out and a call for heat connection which are joined together when heat is required.

What happens when these are joined directly together at the boiler?

Tony

 

[OLLIE20]

If it was me, i would pull the plug of that pump (very simple) and give it a demand, see if it blows the fuse, if not, solved, take about 2 seconds

 

[mikefiore]

Thank you all for your prompt responses.

@45yearsagasman - I thought this wasn't right but thanks for confirming the correct winding resistance. This has proved to be the reason for the fuse blowing.

@Agile - The current measured was through the external pump. The strange readings are on the internal pump. Hopefully this makes it more clear.

@OLLIE20 - good call! Pump disconnected, new fuse inserted, boiler now heating the house back up. Looks like I need to replace (?) the internal pump.

I never really did understand why there are two pumps required. My house is a three bed detached with 9 radiators. It's not massive so shouldn't need two pumps. The external pump is presently managing to pump round the whole house with no issues so I don't think the internal one is really required. Can anyone advise differently?

 

[Garfeild]

What do you mean internal pump? is it an icos system boiler?

 

[mikefiore]

Hi Garfield,

Yes it is an ideal icos m3080 and it has a pump which features in the icos parts list in the installation manual (now at work so can't advise the part number) which is fitted in the lower right hand side of the unit.