bottom stat keep turning off!!

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bottom stat keep turning off!!

Post  sagsy123 on Tue Jun 29, 2010 3:36 am

Strange problem with this pulsercoil 2000, Woke up this morning and found no hot water (off peak timer)checked timer clock work ok and immersion Resistance 18ohms. So I replaced stat it worked for about 2 min then the stat turn off. I tried another new stat different manufacturer still doing same thing. I get power to stat but it just turns off (not cutting out just turning off after couple mins. My booster works but that keeps cutting out so needs resetting everyday.

can anyone help because i cantsee what the problem can be?

Thanks

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Re: bottom stat keep turning off!!

Post  Mike the Boilerman on Fri Jul 02, 2010 3:06 am

Sounds to me as though the store was actually fully hot when you put new 'stat in. It turned OFF because the store was already hot enough!

Does the big brass nut part of the immersion heater feel hot to touch? If so then the store IS hot and the fault lies elsewhere. Is the header tank full? Is the red light on the circuit board blinking twice, once a second?

Mike

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Re: bottom stat keep turning off!!

Post  sagsy123 on Fri Jul 02, 2010 8:03 am

no brass nut was not hot there was no hot water on taps. Hot water only works with booster on but that cuts out when water hot.cant say I noticed the red led light on but the flashing Led lights were indicating normal operation. I was just wandering could it be that the immersion could be badly scaled up, we do live in a hard water area.

Thanks

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Re: bottom stat keep turning off!!

Post  mike on Fri Jul 02, 2010 4:41 pm

Did you test immersion to earth?
When it was working did you test for circuit ( accross the element)
Try swapping the stats over
Also you can swap the peak and off peak supplies in the 2000 ( terminal strip)
So then you will have a supply.
Be careful though!
Mike

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Re: bottom stat keep turning off!!

Post  sagsy123 on Sat Jul 03, 2010 8:00 am

i done resistance check across and got 18- 19 ohms there is power when you turn the timer clock on but only comes on for 2mins and stat turns off! while the power is on there is 240 volts across stat but after stat turns off the power is gone other side og stat. I have tried 3 stats 1 off them being a different manufacturer but same thing happens. how do you do earth test?

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Re: bottom stat keep turning off!!

Post  mike on Sat Jul 03, 2010 6:05 pm

How are you testing the stat, what with.
Are you testing both sides of he stat to neutral ?
This prove you have a circuit.
Test the temperature which should be about 72c
I have had a couple of stats lately which were cutting out far too early and these were new ones.
Did you try the other things I mentioned?
To test to earth try using ohmn meter
Imersion heater terminals you got 18 / 19 ohmns
Test in the same way but to N
And also to earth.
You have 2 immersion heaters so compare the readings.
But be careful as electricity can Kill!

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Re: bottom stat keep turning off!!

Post  sagsy123 on Sun Jul 04, 2010 3:32 pm

Thanks for the help I have tested with multimeter and all circuit seems ok 240v across terminals and to neutral, getting 18 ohms on both immersions I have ordered new immersions and going to fit on friday hopefully this will sort it out.

Thanks for your help i will post back if it sorts it out or not so it can help others.

Any other suggestions as I have already tried 3 new stats one being a different manufacturer. sure they cannot all be duff?

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Re: bottom stat keep turning off!!

Post  Mike the Boilerman on Mon Jul 05, 2010 1:27 am

sagsy123,

I have to say it appears you are now guessing and that is never a good way to diagnose. You HAVE to think about it properly, make sure you understand the tests you carry out and understand the meaning of the results.

It is crucial not to ignore inconvenient results. You say you have tried three different thermostats and they ALL turn OFF after a couple of minutes. This is an inconvenient result, so what does that tell us? The more likely thing it suggests is that all three 'stats are probably working correctly. It is FAR less likely that by chance, all three 'stats have failed with the same fault but this is what you are relying on in choosing to order new heater elements. Further, I cannot imagine a heater element fault that would give the symptoms you describe so this is an interesting problem.

If I were you I'd start diagnosis by getting to understand the fault properly and reproducing it. I'd use my multimeter to measure the resistance across the terminals of one of your three thermostats at room temperature to make sure it is closed circuit (calling for heat), then I'd install it in the Pulsacoil. I'd turn the power ON and wait a couple of minutes for the fault to occur. You say the fault is the thermostat turns OFF after a couple of minutes, so I'd wait a couple of minutes for the thermostat to turn OFF. Then I'd turn the power OFF again and measure the resistance acrss the thermostat terminals again with it still installed in the Pulsacoil and while you believe it to be in it's 'turned off' condition. If your description of the fault is accurate the thermostat terminals will now be OPEN circuit.

This test is designed to prove this really IS the fault. I suspect it isn't, but let's assume it is and the stat is now OFF, and we know this because it is open circuit. How can this possibly happen with the unit cold as you say it is? Try removing the stat and feeling the temp of the rod part (the bit that does the heat sensing). Is it cold? If so, now measure the resistance across the terminals again. Is it still OFF, and open circuit? If so then yes we have a faulty 'stat. If closed circuit then we have a stat that is ON when not fitted in the Pulsacoil and OFF when installed in the apparently cold Pulsacoil. How can this possibly happen? We need to understand. The most likely explanation is that the pulsacoil is actually hot and the heat is turning the 'stat OFF when fitted into place.

Do try this and post the results. You may find you can cancel the order for new heater elements.

Are you sure it isn't the overheat protection thermostast that is tripping? Far more likely!

Cheers, Mike

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Re: bottom stat keep turning off!!

Post  sagsy123 on Mon Jul 05, 2010 7:45 am

I will try your test on friday as I am going away for a few days. can I call you for advice on friday if i have a problem?

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