Immersion heater replacement

Hello people im today had an immersion heater tripping the board.its a sunvic VK 4451.
Ive asked my plumber for a quote but he hasent got back to me yet.
Would this be easy to replace and what is a reasonable quote for a plumber to replace this please.
Its 18” i think.

You can make the job much easier for your plumber Derek if you can stop the cold water flow into the cylinder from your loft tank......can you do that?
Other issues include unscrewing the immersion from the cylinder without damaging the cylinder, and I presume it is an element issue rather than the thermostat?
John

1. The Sunvic Vk4451 is an immersion heater "rod" thermostat, it's not the actual immersion heater.
2. If you want to find out if it is the thermostat or immersion heater (more likely) causing the short circuit, then. if you are comfortable with dealing with lethal mains electricity and you have a multimeter:
2a. Turn off the power at the consumer unit main switch, don't just switch off the circuit breaker for the immersion circuit.
2b. Disconnect all three incoming mains wires, i.e. live, neutral and earth.
2c. Use the multimeter to test for continuity between both terminals of the heater (the brass post in the foreground of your picture) and the body of the heater. If there is continuity, then the heater has gone.
2d. Test the resistance of the immersion (same brass posts) - should be about 18 ohms, but anything between 16 and 20 is OK. If less or more, faulty immersion.
2e. Test for continuity between each terminal of the thermostat and the body of the heater. Continuity = thermostat gone.
3. If its the thermostat, you can replace it without any water contact, it is housed in a sheath inside the body of the immersion, so should be dry.
4. If its the immersion heater, you need to drain off the small amount of water in the top of the cylinder after isolating the cold supply.
5. When reconnecting, make sure all terminals are properly tight.

Thanks for your messages.
Oldbuffer i did all these tests with my tester.
And got no continuity.
And as for testing continuity of immersion i tested between 2 brass posts and got 18ohms.
And tested between the thermostat and body of the heater no continuity.
It all seems all right but,this thing is tripping the fuseboard which is weird

What trips , MCB ,RCD , RCBO ?

Thanks for your messages.
Oldbuffer i did all these tests with my tester.
And got no continuity.
And as for testing continuity of immersion i tested between 2 brass posts and got 18ohms.
And tested between the thermostat and body of the heater no continuity.

Sorry for the double
Post(duh) its an rcb circled in red and rewirable fuses for ring and water heater below.

Using a normal multimeter is often futile for diagnosing RCD faults as the voltages are too low to cause the insulation on the element to breakdown and cause a leakage current to flow to earth.
You could start with the highest ohms range and check the resistance from each element terminal to the brass body...it should be infinite but may be several mega ohms.
The consumer unit is old and the RCD could be suspect however, given the state the immersion heaters can become with corrosion that's probably sensible to replace it as a first option.
Can you isolate the water to the cylinder easily?
I always advise customers of a guide price (and normally quote for a titanium element in hard water areas) but add the caveat that a new cylinder may be required...either the element won't shift, or the threaded flange is chewed up etc. It's a hated job for most plumbers.

Did it trip the RCD ,and NOT blow a fuse ?

Yes the rcd trips but does not blow the rewirable fuse.
The plumber has quoted me £120 seems allright i soppose.the heater is min 20 years old .

Go for it.