Storage heater keeps blowing fuse

[gaz26]

Hi ya guys ,i wonder if you can help me.
Have just been called out to a robinson willey storage heater that keeps blowing the fuse in the cu, it is a combi heater, the convector heater is working fine off the peak but the storage heater on the off peak keeps blowing. Its a 3400w heater.
I have tested it resistance between p and n at the terminal at the bottom and get a reading of 15.2ohms which using the formula voltage squared divided by power and the reading is fine.
ie 230 x 230 = 52900 / 3400 = 15.5 ohms

The resistance on both elements between p and n is 30.3 ohms which i also deem fine.

Also the thermal cut out hasn't tripped so i dont think it has overheated,and both control dials are functioning correctly.

I have also PAT tested the storage side of the heater and it passes fine.

Ive checked the leg back to the cu which is feeding it and this is fine too(This has got its own designated circuit i must add protected by the 15amp cartridge fuse.

I guess what i want to know is ,is there anything else i can do to find and distinguish the fault ? and the only thing now i can think it may be is a dodgy element, which is blowing the cartridge fuse it out when it starts to warm up as this would explain why it PAT tested ok because the tests only last 5 secs .

If it is the element ,how can i tell which one as testing the resistance when it is off,they both have the same reading.

Any ideas would be very appreciated

Thanks in advance

 

[Darkwood]

it is possible a element that shorts out only when its hot, if you cant locate using basic insulation testing etc then try disconnecting one element at a time and see if it cures the problem it may take a couple of nights to sort or you could rig a temp supply on a mcb to check it out, visually check the stat and thermal cutouts too to see if there is any evidence of flash marks, overheated cables etc ...good luck.

 

[mechelec]

have you checked insulation resistance to earth? it sounds as if you have with your pat tester. Also can you use an ammetre to check how much load it is pulling. You should be able to do this on each element and find the faulty one. Good luck