Both immersion heaters tripping in copper water tank

[James Carmichael]

Hi,

I have a traditional copper hot water tank, with two immersion heaters - one powered from economy 7 and a 'booster' one powered from the normal mains. The E7 one (bottom of the tank) is used every night. The booster one has had occasional use. Both were replaced about a year ago. The tank itself dates from the 1990s. We live in a hard water area.

The thermostats on both immersion heaters have a small 'reset' button.

Around about every other morning, the E7 heater needs to be reset. There's normally some hot water in the tank, so it's clearly starting its over night heat up, then tripping.

If I try to turn on the 'booster' immersion heater, that trips too.

The MCBs in the consumer units never need to be reset.

I've placed a multimeter across things. The resistance of the heaters is around 18 ohms, which is what it should be for their wattage. No evidence of issues with the incoming mains supplies (and they haven't been worked on recently).

Any idea what could be causing this?

Thanks

JC

 

[flameport]

Thermostat has failed.
Replace the thermostat.

 

[terryplumb]

Unlikely ,but not impossible ,that both stats have failed. I would think its more likely that the elements are encrusted and the overheat stats are doing their jobs and intervening. What is the temperature of your hot water ,not very hot I guess ??

 

[James Carmichael]

Thanks, both.

The immersion heaters were bought at the same time, from the same shop, and ar ethe same make/model so I guess it's not inconceivable they come from a faulty batch.

Is it likely that both could have encrusted so quickly?

 

[Hot&Cold]

Is it likely that both could have encrusted so quickly?

why not whack one out and have a look

 

[dilalio]

The tank itself dates from the 1990s. We live in a hard water area

You said it yourself... There's the clue ^^

 

[James Carmichael]

Ok, new immersions heaters it is, then. And if the tank is full of crust, new tank too.

I see on line that you can get plenty of tanks with a single immersion heater feeding in from the top. I'm guessing this means I won't have the faff of draining off if I need to replace it again. However, I can't find any tanks with TWO immersion heaters feeding in from the top. Does anyone know if they exist and, if so, could point me to a supplier?

Finally and importantly: Thanks everyone for your replies so far. It's appreciated.

 

[dilalio]

There's a reason for the bottom and top entry points... One is for full cylinder warm up (from base) the other is for top up (From top).