Testing Emmersion element and thermostat Ask questions and find answers to many subjects relating to electrics and electrical work

[Smarty]

Hell all,

Hopefully a simple one...

I changed my hotwater cylinder and emmersion (with thermostat) on March 23rd 2008.
Last night it stopped working, checked fuse etc wiring all clean and ok.
I did notice a very slight whiff of burning (or did I imagine it???)

I have spoken to Wickes who have agreed to change it as I have the receipt providing it is faulty.

The question...

If I check the continuity on the thermostat should it be closed circuit if ok or open when cold? and the same for the element.

Obviously don't want to drag out the element if I can just lift out the thermostat.

Thanks from anyone who knows.

(I did think the thermostat should be a circuit until reaches temp then open, to cut power?0

Smarty 8)

[sparx]

Hi smarty,yup should have a circuit through 'stat at low temp. which breaks at set point temp.
one other point, if switched on with air trapped in tank the over temp. cut out might have tripped, usually very small recessed 'pin' which can be reset with a small pointed object and will make audible click when reset.
It must have one, as it has been illegal to sell immersion heaters with stats that don't have O/T cut outs for about 2 years!!!
regards SPARX

[Smarty]

Thanks Sparx,

I did do a check last night, the thermostat was dead and I got a circuit from the element. I did not know about the reset, but the nice people down at the hardware store changed it for me.

Simple job and now working.

Can I just ask... I am still baffled about why it lasted a month then went, could the air lock have done that?

I did change the tank and emmersion last time, so there is a possiblility air was trapped. Also will it need bleeding or will it have gone by now on its own?

Thanks

Smarty 8)

[sparx]

Hi agn, most likely when drained down for original change some air got in system and collected under element 'dome' probably gone on its own by now. Older good quality elements used to have a bleed screw next to 'stat hole but not seen such for many years now, progress huh!
Do check new stat has got a high temp. cut out fitted, some old stock still in smaller shops. My local store had a mix of types but to the owners credit when pointed out to him by a gas fitter & me later, he threw away those without a cut out!!!
You where lucky yours failed 'Open circuit', if it had failed 'Short circuit' the water would have boiled, hot water would have gone up expansion pipe into cold water head tank. to be replaced by cold water which boils ect. untill cold tank full of scalding hot water! If plastic tank it then melts and dumps several gallons of boiling water through ceiling onto sleeping person below!!! Can't happen? this is from Coroners report into death of a baby and severe injury to person in seperate occurances last year!
Best wishes SPARX

[Mr_fay]

Hi - I was wondering if someone could offer me some quick advice.

I have an indirect cylinder with the immersion heater just screwd in at the top (27"). I had no hot water one morning (nice!) so changed the immersion heater and now I get hot water but no where near a tank full.

I've already put the thermostat on to the highest, hit the reset button and left it running for long enough that it would have previously given me a tank full of very hot water.

The immersion heater wire goes into a fused electrical point and all my water is run through a pump. I have checked the main fuse board as well and that isn't blown, so I am pretty certain that the electrics is all ok. I am thinking it may be to do with the pressure (should I turn off pump and test) and may be that I need to release some pressure but I'm totally baffled as to why I get some hot water. The hot water seems to take a little longer to get to the taps as well (once turned on) than previously. Could this be the case and can you offer advice?

Would be very grateful for any help.

[ericmark]

Both the thermostats and the elements come in diffrent lenghts and some elements fold over at the bottom giving more heat to the lower section. I would guess the new units are shorter than the old ones. Or does not consentrate heat to lower section. Also I think the permitted temperature range has changed now I see 30 - 70 degs but I am sure old ones where 85 degs. I note the Plumbcenter do 30 and 36 inch imersion heaters if the tank is long enough these may help. You also say all your water is run through a pump this is unusual in domestic and normally only used with hotels and circulates the hot water so there is no delay at the taps and you don't have to run off any water in order to get hot water. If you do have this system then longer elements will not help and more likely sedament in the tank is problem. But I have only seen one house with this system and 9 people lived there to give you idea of the size. Are you sure punp is for hot water and not central heating. And if it is for hot water is it running as switching this pump off would reduce the hot water available. I am assuming you don't have a heat store system as normally the elements are fitted through the side not from top. Heat stores work on higher temperatures and have a mixing valve to reduce temperature to the taps so would need the special imersion designed for the system and not a standard one. They also sometimes work with higher pressures and there is a licence system to be able to work on them.

[Mr_fay]

Thanks for the help. I think it basically turns out that the new immersion heater is no where near as good as the old one. We basically have some old hot air system for our heating and then this immersion heater on the tank for the hot water. Kind of decided that its a bad system and as everything is 20\30 years old, its best that we just live with it for a couple of months and get it all changed. We're getting hot water, so will just have to plan the showers!!!!!!

Really appreciated the reply.

Martin