Myson Kickspace plinth heater fuse keeps blowing whenever it comes up to temperature

[michael123123]

I've just installed a new Myson Kickspace 600 plinth heater. The heating side of it is working fine - gets good and hot throughout all the pipes. In terms of the electrical connection, it works fine before I turn the heating on. In Summer mode, the fan switches on successfully. However, after a bit of trial and error, it seems that when switched to Winter mode and the heating is turned on, the fuse blows when the heater reaches temperature and the fan never turns on.

I've tried both hardwiring it to a switched FCU as well as putting a 3 pin plug on the flex (with a 3A fuse). Peeking inside the unit, I can't see any damaged wires or any obvious damage.

What can I do to further isolate the problem and go about fixing it?

 

[ericmark]

It seems likely a fault on the low limit stat, as it is about the only thing used in winter mode which is not used in summer mode.

 

[michael123123]

A 3 amp fuse is only good up to 720 watts. A plinth heater will be one or two kW. Use a 13 amp fuse.

The heater I mentioned in the original post is a hydronic heater. The only electrical bit is the fan and this only requires a 3A fuse, as specified in the installation instructions.

 

[jj4091]

As Eric said, & according to the circuit diagram, it would appear to be the stat or the wires leading to it. Try disconnecting it & shorting the leads together. If it still blows try disconnecting the black lead to the fan & if it's then OK it would suggest the fan is faulty

 

[ericmark]

A 3 amp fuse is only good up to 720 watts. A plinth heater will be one or two kW. Use a 13 amp fuse.

No it is not, it is a hydraulic type, heating is done by the central heating, the fuse only protects the fan, a 1 amp should be enough. You can clearly see the heating pipes in picture two.

 

[ericmark]

As I said to the OP I accept it is not a resistive heater, but the fuse is not to protect the fan, it is to protect the cable.

With a portable appliance that is true, but with a fixed appliance the manufacturer is free to stipulate what external controls are required, quite common for motor starters not to be integral with the equipment but located else where convenient for the operator to use, do not get the rules for portable mixed up with fixed, they are different.

 

[EFLImpudence]

If products require internal fusing then the manufacturer will fit a fuse; if they have not then one is not required.

 

[ericmark]

If products require internal fusing then the manufacturer will fit a fuse; if they have not then one is not required.

I have worked on many industrial machines where the fuse is stipulated by the manufacturer, often special semi-conductor fuses where solid state relays used.

With a 13 amp plug yes the fuse is to protect the cable only, as we were members of the EU and plugs could be removed and different EU plug fitted, so we were the odd one out with fuses in the plug. But that does not follow for installed equipment, for example the new English landlord law makes it part of the EICR testing when installed, be it wall fan or immersion heater, but items not fixed would be tested with the PAT testing (inspection and testing of in-service electrical equipment).

I agree even a 1 amp fuse would likely blow after the winding of a stalled fan, so is a little pointless for equipment protection, but my Myson fan assisted fan stalled without damage to windings, maybe due to position of the massive rheostat to control fan speed, but it had been in my house some 30 odd years so they are quite robust.

Not much in them, a thermostat which turns it on/off as room heats up, a fan, a rheostat, and a thermostat on the pipe so it only runs when the pipes are hot. I think the plinth model does not have the rheostat? I modified mine to work as a fan in summer, was not standard.

The new ivector model is another story with a 5 speed fan which auto adjusts speed depending on return air temperature ability to connect to building management system can have single or twin heat exchangers and can be connected to a heat pump to heat and cool the room, a really nice bit of kit, but the one shown is rather simple, don't think they have a condensate pump so can only be used to heat with.

 

[EFLImpudence]

I have worked on many industrial machines where the fuse is stipulated by the manufacturer, often special semi-conductor fuses where solid state relays used.

Maybe, but we are dealing with household appliances.

 

[Adam_151]

@michael123123 The wiring looks differnt from the drawing, but I can't properly see what goes where, particualy the blue cores and the layout of terminals on the switches, could you annotate to show where conductors are connected, and take a pic with the camara above the motor looking at the back of the switches.

I'm guessing the stat is putting a direct short across the supply, but arguably if it is new and its come incorrectly wired, then you should just send it back...

 

[michael123123]

The wiring looks differnt from the drawing, but I can't properly see what goes where, particualy the blue cores and the layout of terminals on the switches, could you annotate to show where conductors are connected, and take a pic with the camara above the motor looking at the back of the switches.

I'm guessing the stat is putting a direct short across the supply, but arguably if it is new and its come incorrectly wired, then you should just send it back...

That's an interesting observation... I've labelled the wiring in the attached photo. For reference, the red arrows correspond to the fan selector switch and the yellow arrows correspond to the summer/winter switch.

It looks like connectors (b) and (d) are swapped! In its current configuration, when it's set to winter and the thermostat switch is closed (i.e. up to temperature), the thermostat loop connects the supply live and neutral. If my understanding is correct, then that would cause the fuse to blow.

I'm away at the moment, so I'll have to wait before I can prove this to be true or take any further photos of the heater.

Another thing I just noticed is the is an "N" with an arrow labelled on the summer/winter switch visible in the wiring diagram photo. This label appears to be pointing to stat/motor blue wires, but I wonder if the supply (neutral)/stat blue wires should be attached to that terminal.

 

[SUNRAY]

A 3 amp fuse is only good up to 720 watts. A plinth heater will be one or two kW. Use a 13 amp fuse.

SO SO TYPICAL of your know nothing ignorance winston1noon gulf

 

[bernardgreen]

Back to original question

It looks like that thermostat has been soldered to the heating pipe. If the metal of the stat has been soldered to the pipe then the heat from the soldering is likely to have damaged the thermostat

 

[bernardgreen]

Who is this Sunray person who seems to only be capable of being rude and disrespectful?

Sunray is an experienced and competent engineer.

 

[SUNRAY]

Back to original question

It looks like that thermostat has been soldered to the heating pipe. If the metal of the stat has been soldered to the pipe then the heat from the soldering is likely to have damaged the thermostat

I thought I'd sent the following reply earlier but it was still sitting here:

If the unit is wired according to that diagram I see nothing that can give the symptoms you describe other than component failure and the only component I can envisage doing that is the thermostat. I imagine it may be shorting to the metal case when it operates. It's a bit tricky from the photo but are you able to verify it is all correct?

Seeing the way the thermostat is mounted on the heat exchanger it could have easily been overheated during manufacture.

The way the system works in heating mode is is different to how many expect; when the heat exchanger reaches temperature the thermostat kicks in and runs the fan to circulate warm air.

EDIT:
The next test to do is run the heating up to temperature with the switch set to summer so the fan runs and see what happens when it reahces temperature NO DON'T...Just noticed it's wired wrong and thank you for the annotation! I'll have another look and get back

EDIT 2:
Thank you again for your Brilliant annotation and Adam (now that I've checked more of the thread). What has happenned is a silly 'schoolboy error' during manufacturer; the connectors on the supply cable are on the wrong terminals, the whole of Supply Blue + Stat Blue (b) needs to be exchanged with Supply Brown (d).

Good luck