Older storage heater element resistance measurements.

The elements in most older storage heaters were 850w per element. If it is suspected that the heaters output is not what it should be, an electrician can check that all elements are working as expected by performing a resistance check on the elements. 

This article applies to the following models:

Applicable to: XL12 XL18 XL24 XL12N XL18N XL24N XLS12 XLS18 XLS24 XLS12N XLS18N XLS24N XL6 XLS6 XLS6N, TSR6MW TSR12MW TSR18MW TSR24MW TSR6AW TSR12AW TSR18AW TSR24AW TSR12ACW TSR18ACW TSR24ACW CLX12 CXL18 CXL24 CXL12N CXL18N CXL24N CXLS12N CXLS18N CXLS24N NL10575 NL10576 NL10577 NL10578 NL10579 NL10580 NL10581 NL10657 NL10658 NL10659 NC1700AUTO NC2550AUTO NC3300AUTO NC1700COMBI NC2550COMBI NC3300COMBI STHS170A/09 STHS255A/09 STHS330A/09 STHC170A/09 STHC255A/09 STHC330A/09 STHS085/09 AC6810 AC6811 AC6812 AC6813 AC6814 AC6815 AC6816 AC6817 AC6818 AC6819 WMX706N WMX712N WMX718N WMX724N WMS712N WMS718N, WMS724N WMCS712N WMCS718N WMCS724N

It does not apply to the current Quantum or XLE/Slimline models. Details for those models can be found here.

WARNING. The appliance must be safely isolated from both mains supplies and proven dead before carrying out any work!  

The elements in older storage heater are wired in parallel like this:

An electrician can test if all the elements are OK or not, by disconnecting the heater from the mains supply, turning the input dial to maximum on the heater, then measuring the resistance on the mains terminal block of the heater. The resistance value would then read as follows depending on the size of the heater.

If the reading is higher than expected, it may signify an element has failed, so the cover of the heater then needs to be removed and each individual element resistance reading checked to identify the element possibly at fault. 

If the reading is infinate or ---- on the meter (the same reading as when the multimeter probes are not touching each other) then it may be that the thermal cut-out on the heater has tripped and may need resetting, or the input thermostat is not set to maximum / not working correctly. Check resistances of individual elements to verify them and continuity test the thermostat / cut-out circuit to verify which component is open circuit. 

If an insulation resistance test is performed on elements, it can be done tested to 500v and would be tested between element sheath and element terminal and the anticipated insulation resistance would be at least 1Megohm. As the elements are mineral insulated, running the element for a few hours can often drive out any moisture and the element may then return to >1Megohm insulation resistance if seen to be below this on an initial test.

Note these models are no longer available, therefore spares may be limitedIf spare parts are required, see this link.