The rod is most likely invar which has a low expansion coefficient, and obviously the tube is brass with a high expansion giving the required motion to operate the contacts.

Destructive Analysis is under-rated. No better way to understand a component and be able to understand the integration and possible repair. I wish there were more DA videos out there. Thanks!

those thermal discs are incredibly reliable. they are used in many boilers as overheat thermostats for years.

these videos should be the benchmark for all tutorials on UT.

Thanks, man. I fixed the thermostat at my house because of your videos.

you poked my eye out at start of video

+John Ward Brass has a higher expansion coefficient than steel, so surely the brass case will pull the rod away from the housing rather than the rod expanding and pushing in?

@Bob_Burton

8 жыл бұрын

Good thinking.

@jwflame

8 жыл бұрын

Yes, it's the opposite to what I said in the video.

@SteveBrace

8 жыл бұрын

+John Ward Sorry... My chronic pedantry wouldn't let it go :) Your punishment is to subscribe to me :)

another great video, very helpful....I have two thermostats top and bottom that both click when turning the dial and when powered I can hear that one is working but both give the same reading with the multi meter regardless of the position of the dial... any thoughts

Very interesting indeed. I have never dissected one of these, about as sophisticated as an old toaster! Many thanks for posting, another excellent video.

Hi John, would polarity of the terminals matter in the thermostat? I don't mean where incoming mains neutral and cpc are attached. Just the two terminals on the stat where mains incoming line is attached to one side.

Failure is the brass outer was not crimped correctly, and slipped on the plastic, losing the tension in the inner rod. Take the spring bimetal and warm it with some heat ( place on a clean frying pan and turn on the heat) and it will pop off at 90C.

I've just realised with the thermostats that I've been buying that it's not necessarily the stat that fails but the metal wheel that goes slightly out of sinc with the plastic adjustment wheel on the outside of the stat, it seems like one certain manufacturer whom I've been using does not fix these with a heat resistant adhesive and this in turn stops the contacts from working, this has been somewhat of a revelation as I now have 4 fully functioning stats and all they needed was a slight adjustment and some high temp super glue,faulty or just poorly manufactured????

Hi john i discovered the other day my hot water is only slightly warm even with the cylinder thermostat fully up it was on for a while but still just warm , is that a thermostat at fault on the cylinder or would it be the immersion heater thermostat or element, i have checked there is no loose wiring and the is voltage on the cable before the thermostat itself on the cylinder ,can i test each thermostat with my meter any help would be great

very intresting on how basic they are.

Hi John, I appreciate all you videos. Have you got a video on the Calculation of SWA Sheathing as an earth. Rgds. Peter.

@russelltwells4747

5 жыл бұрын

The outer sheaf up to 16mm squared conductors,over 16 mm,run an earth,as a rule the same cross sectional area as the sea,conductors ,hope it helps

hello, do they all work by the same principle? is stem and rod thermostat the same thing ?

Great video,very informative and well presented, thank you

When you turn the temperature setting dial early in the video you note that there is no click at any point. Bearing in mind the temperature range of the dial would you expect the contacts to open at any point in a normal environment ?

@jwflame

8 жыл бұрын

They all click when the dial is rotated, even when cold. The temperature markings are not very accurate at the lower end of the scale.

Thank you John, I would like to ask you a question. The top thermostat on our immersion heater is upside down and wired the wrong way around. Would that make a difference, stop it working? The water is very hot...

@jwflame

3 жыл бұрын

No difference, all the thermostat does is connect the two wires together when heat is required.

At about 5:55 you show the white plastic piece moving in and out to open and close the contacts. To open the contacts the plastic piece has to be pushed in which to me implies that the long rod needs to get shorter when heated in order to pull the plastic piece and turn off the power. This seems odd. Have I misinterpreted what I am seeing ?

@MiesvanderLippe

8 жыл бұрын

The brass needs to get longer in comparison to the inner rod.

@Bob_Burton

8 жыл бұрын

Good thinking.

Thanks, I thought the tube would be filled with some type of wax, but I guess it's aluminum or invar.

since changing mine....i am contantly pressing re-set button....i,ve set it at 55-60 ?

@jwflame

7 жыл бұрын

Either the new thermostat is defective, or there is some other heating source causing the temperature to rise above 90C. Entirely possible for new thermostats to be broken or damaged, particularly if they are supplied without packaging.

what would happen if you put a shorter stat in.would the tank still heat up

@jwflame

8 жыл бұрын

It would heat up, but the thermostat would switch the heater off before all of the water was heated as it would react to the temperature near the top of the tank only.

Are there immersion heaters designs where the thermostat is not removable? My thermostat is faulty (always on) and seems to be fixed in place. I am reluctant to pull on it too much for fear of breaking it. This was installed in 1997. Thanks for any advice.

@jwflame

10 ай бұрын

Not that I know of. It's either the style shown in this video, or unvented cylinders typically have a larger thermostat head which plugs into contacts on top of the heating element. Either way, both are designed to be replaced.

would a faulty thermostat cause the water to not heat up to the required temperature my tank is only heating a small amount of water

@jwflame

3 жыл бұрын

Yes, if it's switching off at a low temperature.

Hello mate. I have a pullin h8 thermostat, 15 amp 250v on my emersion heater. I have recently changed the isolator switch on wall as it stopped working. (Wasn't switching on). Now it stopped working again last week , so when I opened the cover on the heater and turned the water temperature down to minimum setting 120f, I heard it 'click' and it started working again for a week. A week later it's stopped working. Am I right in assuming the thermostat is faulty . And are they all the same or will I need the exact same one. Also instead of leaving it " on" at the wall all the time I tend to switch it off and on when needed. Is this not good to do? Thanks in advance

@jwflame

5 жыл бұрын

99% faulty thermostat - 120F is far too low for normal use anyway. The fact it's marked in F means it's probably decades old. They are all basically the same, the only real difference is the length of it, you need to get one of the same length. If it fits into the top of the cylinder probably 18", or 11" if it's in the side - but this will be obvious when you take the old one out. Doesn't make any difference switching it on/off.

@moshazza5684

5 жыл бұрын

@@jwflame thank you for prompt reply. Yes it's the top of the tank. I will remove it and check length . I have taken a pic of the top of it, but can't attach, but I think it's a case of disconnect the two wires and it just pulls up/out maybe a little help from prising it with a screwdriver?

@jwflame

5 жыл бұрын

@@moshazza5684 Yes, it should just pull out, no prising required.

He doesn't seem to know what he is doing himself !!! Chancer.

Fell asleep....inconsistent mumble...mumble...mumble with vaious degrees of soporific.....? mumble !!!