3KW Water Heater Wiring

[Ash4eva12]

Hi all!

Quick question regarding a "Zip aquapoint 3 (III) water heater" wiring.

Problem is the thermostat (part no. AQ0319) has burnt out / melted at spade connections & the power supply never tripped.

The 3kw water heater is fed by 2.5mm t+e from a 16a mcb in consumer unit then directly to a FST77 13a fused timegaurd 7 day programmer with a 2.5mm HR flex to water heater. (someone has removed the old 13a spur and replaced with the timer)

so for a start should this have a means of local isolation which seems to have been removed when they fitted the timer such as a 20a DP switch between the supply and the programmer?

Also is the timegaurd sufficient with a 13a fuse built in? Or would it be better to fit something such as a NTT03 rated at 16a with no fuse protection?

Any help would be much appreciated!

Thanks.

 

[pc1966]

The over-current protection will only trip if there is an over-current fault, a bad connection leading to the thermostat overheating would not be detected.

I have never seen one of those FST77 thermostats before but it looks like it is intended as a FCU replacement as it has both a fuse and DP switching for the load. From a quick look at its instructions it seems there is no need for additional isolation.

If it were me I would just replace the thermostat but carefully check all of the connections are clean and tight in case there is something else that is a pending fault, and that the related cable(s) have not been damaged by the heat.
[automerge]1587730491[/automerge]
Remember that with just 0.05 ohm excess resistance and 13A flowing you are getting over 8W of heat, that is not good for any terminal!
[automerge]1587730750[/automerge]
If it is the same as this one sold by screwfix then it is 2kW rated:

Zip Aquapoint III AP3/10 Electric Water Heater 2kW 10Ltr - Screwfix

Order online at Screwfix.com. Undersink, unvented 10ltr water heater for single or multiple outlets. Features sacrificial anode for protection against corrosion, external temperature control with frost protection and high performance polyurethane foam insulation. Suitable for use with...

www.screwfix.com

 

[Ash4eva12]

The over-current protection will only trip if there is an over-current fault, a bad connection leading to the thermostat overheating would not be detected.

I have never seen one of those FST77 thermostats before but it looks like it is intended as a FCU replacement as it has both a fuse and DP switching for the load. From a quick look at its instructions it seems there is no need for additional isolation.

If it were me I would just replace the thermostat but carefully check all of the connections are clean and tight in case there is something else that is a pending fault, and that the related cable(s) have not been damaged by the heat.
[automerge]1587730491[/automerge]
Remember that with just 0.05 ohm excess resistance and 13A flowing you are getting over 8W of heat, that is not good for any terminal!
[automerge]1587730750[/automerge]
If it is the same as this one sold by screwfix then it is 2kW rated:

Zip Aquapoint III AP3/10 Electric Water Heater 2kW 10Ltr - Screwfix

Order online at Screwfix.com. Undersink, unvented 10ltr water heater for single or multiple outlets. Features sacrificial anode for protection against corrosion, external temperature control with frost protection and high performance polyurethane foam insulation. Suitable for use with...

www.screwfix.com

Hi

Thanks for your response the model number is AP3/50 ... Its the 50 Litre one rated at 3kw
[automerge]1587731137[/automerge]
Theres a photo of the burnt out thermostat

 

[westward10]

Both of those connections have over heated obviously one more dramatic than the other. That is more than a case of replacing the stat.

 

[David Prosser]

If I was you I'd look at replacing the whole thing. We have quite a few of those dotted around the place. I've replace diffrent bits in them (normally furred up heater part) but it nearly allways fails on another bit within a couple of months. You end up spending more time and money than if you just fitted a new one.

 

[pc1966]

How old is it?

If it is more than 2 years or so old I would follow David Prosser's advice and replace the whole thing.

If repairing it then obviously both wires need to be replaced and terminals properly crimped on (ratchet tool, not those horrible multi-purpose ones you get with sets of terminals!). Can you disconnect the ends of the cables easily enough?

 

[pc1966]

Your call obviously to repair, but would be nice to hear back how you get on with whatever path is taken.
[automerge]1587760254[/automerge]
Also just to comment on the lack of isolator switch: the fact it has a dedicated MCB should be sufficient for an electrician to deal with it and the end user can still isolate the load using time-switch's rocker, but it would not be a bad idea to make sure both the MCB and the time-switch are properly labelled to indicate this (assuming the customer is not the sort who refuses labels even if it will cause trouble down the line).