Geekzone: technology news, blogs, forums
Guest
Welcome Guest.
You haven't logged in yet. If you don't have an account you can register now.


4 posts

Wannabe Geek
+1 received by user: 1


Topic # 230303 17-Feb-2018 16:44
Send private message

My electric hot water cylinder is on controlled power, I believe it turns on about 11pm daily.
For the last two days at about 5am, hot water has been pouring out from the standpipe, because the water in the cylinder has got so hot.

 

In order to stop the overflowing, I switched off the cylinder power switch and opened a hot tap for a few seconds.

 

I used a multi-meter to check a few things:  With the wires disconnected, the element is 35 ohms between terminals, and open circuit from each terminal to the metal cylinder casing or earth.  So apparently the element is fine.
The earth and neutral test as a good connection, via the MEN link at the switchboard.  So no broken earth or neutral wires, at least in the HW circuit.
Later, when the temperature was no longer crazy-hot, I also checked the thermostat, which is a T80 ST107.  It behaves as expected, open-circuit at a low setting, closed-circuit at a high setting.  Each thermostat terminal is open-circuit to the cylinder casing.  So apparently the thermostat is fine.

 

The low pressure cold water supply, after the nefa valve, enters via a tap underneath the cylinder.
The low pressure hot water outlet from the cylinder (to taps and standpipe) I expect is on top of the cylinder.  It's out of sight, within the ceiling space.

 

About a month ago, I replaced the nefa valve entirely, because the diaphragm had perished.  So I hope the nefa valve isn't the cause of the current issue.

 

YouTube tells me that Americans ought to flush their cylinders every few months (I think due to sediment and/or minerals and/or calcification).
I wonder if we have this issue and should follow this practice in NZ?
I've only been in my Whangarei home for 4 months.  Aside from the perished nefa diaphragm, I have no indication as to the age of the cylinder.
Even if my cylinder has sediment around the element or thermostat, I can't quite see how that might cause my issue.

 

At this stage, I'm thinking I should drain the cylinder, then replace both the element and the thermostat.
This may be tricky, since there isn't a dedicated 'drain' valve/tap (unless it's the garden-style tap located inside the garage).  I'll need to disconnect the pipe below the 3/4" brass tap, then connect my garden hose.

 

Does anyone have thoughts as to what the issue may be?


Filter this topic showing only the reply marked as answer Create new topic

Stu

Hammered
5045 posts

Uber Geek
+1 received by user: 1062

Moderator
Trusted
Lifetime subscriber

  Reply # 1959649 17-Feb-2018 17:17
2 people support this post
Send private message

Are you sure it's 'boiling over'? Might simply need to adjust the Ajax valve below the cylinder. Turn it back a quarter to half a turn, anti-clockwise and see if that works. Might have to come back a bit further again, until it comes right.




Keep calm, and carry on posting.

 

 

 

Click to see full size Click to see full size


2413 posts

Uber Geek
+1 received by user: 704

Trusted
Lifetime subscriber

  Reply # 1959656 17-Feb-2018 18:08
One person supports this post
Send private message

If the thermostat has failed, the cylinder won't maintain a steady temperature and will either boil or go cold.  We've had this happen and had the cylinder boil.  You can hear it when standing close to the cylinder.

 

I believe a Sparky replaces this not a plumber as the thermostat sits in a cavity and does not get wet.





"4 wheels move the body.  2 wheels move the soul."

“Don't believe anything you read on the net. Except this. Well, including this, I suppose.” Douglas Adams



4 posts

Wannabe Geek
+1 received by user: 1


  Reply # 1959659 17-Feb-2018 18:16
Send private message

Stu: Are you sure it's 'boiling over'?....

 

Thanks for your reply Hammered.  The tap water has been scalding hot today, even the casing on the cylinder was quite hot to touch initially.  When I replaced the ajax valve a month ago, I allowed plenty of leeway with this adjustment.


Stu

Hammered
5045 posts

Uber Geek
+1 received by user: 1062

Moderator
Trusted
Lifetime subscriber

  Reply # 1959660 17-Feb-2018 18:17
Send private message

You'll be needing a sparky then.




Keep calm, and carry on posting.

 

 

 

Click to see full size Click to see full size




4 posts

Wannabe Geek
+1 received by user: 1


  Reply # 1959663 17-Feb-2018 18:32
Send private message

Dynamic: If the thermostat has failed...

 

Thanks for your reply Dynamic.
Yes I could hear the boiling at the cylinder, as well as the standpipe overflowing.

 

I'm going down the thermostat replacement route.  Partly because (despite my meter telling me the thermostat was ok) it seems the most likely culprit and doesn't involve draining the cylinder.  Perhaps it has an intermittent fault (my favorite kind).
Thankfully Mitre 10 Mega (my favorite shop) was open.  $86.30 later, ouch.

 

So I'll know if this works at about 5am tomorrow.


Dangerous Chocolate
158 posts

Master Geek
+1 received by user: 37

Subscriber

  Reply # 1959720 17-Feb-2018 20:53
One person supports this post
Send private message

SpikerBrian:

 

Dynamic: If the thermostat has failed...

 

Thanks for your reply Dynamic.
Yes I could hear the boiling at the cylinder, as well as the standpipe overflowing.

 

I'm going down the thermostat replacement route.  Partly because (despite my meter telling me the thermostat was ok) it seems the most likely culprit and doesn't involve draining the cylinder.  Perhaps it has an intermittent fault (my favorite kind).
Thankfully Mitre 10 Mega (my favorite shop) was open.  $86.30 later, ouch.

 

So I'll know if this works at about 5am tomorrow.

 

 

Welcome to Geekzone :-)

 

Yes I would have suggested thermostat first, as it's easy and (relatively) inexpensive. I just replaced the thermostat on a 3 week old cylinder, it was staying open circuit even though it was "ticking" at the right place when turning the adjustment knob.

 

Cheers

 

 




4 posts

Wannabe Geek
+1 received by user: 1


  Reply # 1959776 18-Feb-2018 08:18
One person supports this post
Send private message

Virgil:

 

Welcome to Geekzone :-)

 

Yes I would have suggested thermostat first, as it's easy and (relatively) inexpensive. I just replaced the thermostat on a 3 week old cylinder, it was staying open circuit even though it was "ticking" at the right place when turning the adjustment knob.

 

Cheers

 

Thanks Virgil.  Fancy seeing you on here :)

 

Success!  The thermostat replacement resolved the problem.
Although, it's still annoying me that the meter testing (along with the "ticking") showed it as perfectly fine, haha.  I suppose there are various modes of failure.

 

Thanks to the other guys too.  Geekzone is a great forum, I'm glad I finally joined.


4966 posts

Uber Geek
+1 received by user: 1578


  Reply # 1959793 18-Feb-2018 09:10
One person supports this post
Send private message

You could test the thermostat in a pot of hot water with it removed.


Filter this topic showing only the reply marked as answer Create new topic

Twitter »

Follow us to receive Twitter updates when new discussions are posted in our forums:



Follow us to receive Twitter updates when news items and blogs are posted in our frontpage:



Follow us to receive Twitter updates when tech item prices are listed in our price comparison site:





News »

Intel introduces new NUC kits and NUC mini PCs
Posted 16-Aug-2018 11:03


The Warehouse leaps into the AI future with Google
Posted 15-Aug-2018 17:56


Targus set sights on enterprise and consumer growth in New Zealand
Posted 13-Aug-2018 13:47


Huawei to distribute nova 3i in New Zealand
Posted 9-Aug-2018 16:23


Home robot Vector to be available in New Zealand stores
Posted 9-Aug-2018 14:47


Panasonic announces new 2018 OLED TV line up
Posted 7-Aug-2018 16:38


Kordia completes first live 4K TV broadcast
Posted 1-Aug-2018 13:00


Schools get safer and smarter internet with Managed Network Upgrade
Posted 30-Jul-2018 20:01


DNC wants a safer .nz in the coming year
Posted 26-Jul-2018 16:08


Auldhouse becomes an AWS Authorised Training Delivery Partner in New Zealand
Posted 26-Jul-2018 15:55


Rakuten Kobo launches Kobo Clara HD entry level reader
Posted 26-Jul-2018 15:44


Kiwi team reaches semi-finals at the Microsoft Imagine Cup
Posted 26-Jul-2018 15:38


KidsCan App to Help Kiwi Children in Need
Posted 26-Jul-2018 15:32


FUJIFILM announces new high-performance lenses
Posted 24-Jul-2018 14:57


New FUJIFILM XF10 introduces square mode for Instagram sharing
Posted 24-Jul-2018 14:44



Geekzone Live »

Try automatic live updates from Geekzone directly in your browser, without refreshing the page, with Geekzone Live now.



Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly to your computer or smartphone by using a feed reader.

Alternatively, you can receive a daily email with Geekzone updates.