Siddons heatpump thermostat errors « Alternative Technology Assn Forums

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Siddons heatpump thermostat errors

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Started 3 years ago by Bushwalker
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Bushwalker
Member

Hi.
We have had a Siddons heatpump system for years, and have been excellent. 320L with a separate compressor system.

Derwent T2A and temp set is at 57C

In the last year or so, the thermistor on the water tank has been failing. We call in the local hot water guy and he checks the system, resets the button on the compressor and it runs ok until the thermostat over heats the water and the button pops off again. Removing the thermostat, the package is loose and the top can be moved around the base. A new thermostat is solid and it works 100% until the cap gets loose in weeks or months and the problem returns. The cap is connected to the base with 4 clips, not welded or significant crimp.

Asked Derwent if I could buy a box of them so I can fix the issue easily, and yes I can buy them but the price is $75 each plus GST and freight. It's just a bimetal temp gadget with no electronics, poor manufacturing and outrageous pricing!

So now looking at options. We know the compressor is working 100%. The tank heats fine but the thermostat is the failing problem. Looking for an alternative, found a Temp controller with a temp sensor and a 240v relay and an adjustable temp: https://www.ebay.com.au/itm/281280638271

Have ordered one of these to test. The controller has a 10A 240v relay, and I hope it is adequate but given the Derwent is a failure I expect that is a minor issue. If it has an issue, I could add a 15A relay.

Any suggestions or options I should be looking at other than replacing the whole system because of a silly thermistor?

Posted Monday 29 Jan 2018 @ 12:28:49 am from IP #
Benny
Member

you say its a thermistor but then say its just a bimetal temp gadget ? I'm confused. Which is it ?

Posted Monday 29 Jan 2018 @ 2:21:04 am from IP #
Bushwalker
Member

Well, it is a bimetal device and called a thermostat by Derwent. So not a thermistor But called a thermistor in some of the Siddons documents.

http://www.derwentthermostats.com.au/images/products/T1_0001.pdf

Regardless, it does not work reliably on our system.

Posted Monday 29 Jan 2018 @ 2:31:48 am from IP #
Bushwalker
Member

Corrected the names, thanks Benny.

Posted Monday 29 Jan 2018 @ 2:51:17 am from IP #
Benny
Member

I thought it would be a thermistor - so it can measure the temperature and compare to manifold temperature. A bimetal thermostat can't do this.
Do you have both on the system ? A thermistor to measure temp and control the pump and a bimetal thermostat to turn the whole thing off if temp exceeds a specified max ?

Posted Monday 29 Jan 2018 @ 5:22:01 am from IP #
Bushwalker
Member

Nope. It is a bimetal device attached to the water tank about 2/3 up the tank. The heatpump compressor will run when the water temp is lower than the device (57C) and the offpeak power is on. When the water temp at that location gets to 57C then the bimetal device switches off the heatpump. Water temp can drop a few degrees (I think 5C) before the bimetal clicks back on.

No manifold. It is a heatpump system, not a solar or heatpump/solar system.

Posted Monday 29 Jan 2018 @ 6:10:44 am from IP #
Benny
Member

Sorry BW - getting my wires crossed. Mixed up with another thread on solar HWS.
You can get simple thermostat switches from Jaycar - $6. 10A 240V. Lots of temp options too.

https://www.jaycar.com.au/60-c-thermal-circuit-breaker-switch/p/ST3821

Posted Tuesday 30 Jan 2018 @ 1:17:21 am from IP #
Bushwalker
Member

yep, there are quite a variety, but no 57C. Also a lot smaller than the Derwent so would be more difficult to attach to the hot water tank.

Running at 60C uses more power. We don't run out of hot water at 57C. 50C might be too cool, there is a 55C on ebay though. If the controller doesn't work well, will try the switches.

Posted Tuesday 30 Jan 2018 @ 2:45:54 am from IP #
scott drew
Member

There's a regulation/code/standard as to how hot hot-water in tanks needs to be heated to prevent health issues. Not sure of the temp but it may be relevant.

SD

Posted Tuesday 30 Jan 2018 @ 8:39:08 pm from IP #
amun-ra
Member

For safety stored water is must regularly hit temperatures over 60 degrees to inhibit growth. To this end, the auxiliary booster is best left permanently on. A solar water heater system under AS 3498 must ensure that "at least 45% of the water contained within the storage tank is heated to a minimum of 60C daily".Clipped from an earlier post

Posted Tuesday 30 Jan 2018 @ 8:56:12 pm from IP #
Bushwalker
Member

Correct, the temp in the tank needs to get to 60C

The Siddons tank temp reaches above 60C at the top of the tank. The temp device is mid area of the tank at 57C. That is normal for that system and would have been approved.

The Siddons system does not have an auxiliary booster. Only heated by heatpump.

Posted Tuesday 30 Jan 2018 @ 10:44:12 pm from IP #
Bushwalker
Member

The 220-240V Temperature controller arrived today, and I set it up at 57C and have connected the temp sensor to the tank next to the standard bimetal thermostat switch. No direct connection to to the compressor yet, just testing the temp today/tonight. Had to reset the heatpump so it will run again tonight.

The controller off to one side of the tank showing the current temp at the tank:

And the 57C setting on the controller:

Will see how it displays the temp tonight. Be interested if the temp goes high causing the reset on the compressor switch.

Posted Wednesday 31 Jan 2018 @ 8:08:24 am from IP #
Bushwalker
Member

While sorting out the area to fix the temp sensor to the tank, I removed the Derwent thermostat to check the area beside it was in the same situation (it is). The conductive paste there was dry, and part of it fell off when I inspected it. Also noticed the Derwent was not strongly attached (it uses springs on the threads, but not firmly screwed down) When I replaced the Derwent, I screwed it down a lot firmer than it was when I removed it, and moved it around so it sits flat on the dry paste.

After running the compressor, I was expecting it to run well over 57C and the system switch off via the fuse relay on the compressor, but it didn't - the temp ran to 57.6C and switched off as it should normally.

Now I will run it normally and see if the extra tension on the thermostat solves the thermostat errors over the next few days. If so, then I will keep the Derwent running and the electronic controller as a backup if the Derwent fails. Probably should replace the conductive paste too if things continue to work ok.

Posted Thursday 1 Feb 2018 @ 6:30:09 am from IP #
Bushwalker
Member

lol. And it tripped overnight. Will be back onto the original plan

Posted Thursday 1 Feb 2018 @ 11:33:49 pm from IP #
scott drew
Member

Bushwalker, have you contacted siddons on this issue? I thought the reset button in the compressor cabinet was protection for the compressor due to lack of gas in the system (although it may have other purposes too).

When mine was installed it waa done by someone who had never done a siddins before. He didn't tighten the gas lines properly so it leaked out. Air con guy came to fix, tightened gas lines, refilled gas and reset the lot by pressing the red button. Worked like a charm ever since.

Are you sure your button is popping due to the thermostat?

If you haven't called siddons yet to discuss it, I would suggest you do.

SD.

Posted Friday 2 Feb 2018 @ 1:34:54 am from IP #
Bushwalker
Member

Hi Scott,

Yes, tried calling Siddons, but the business has been moved and do not reply. Left messages etc but no reply.

Our system has been checked many times over the year. Gas and gas lines are 100%, compressor 100%. The fault is the thermostat multiple times, and they fail.

Posted Friday 2 Feb 2018 @ 1:52:23 am from IP #
Bushwalker
Member

Also, if there is a system problem, eliminating the thermostat issue will eliminate it as the issue.

Each time the thermostat fails the device has physically changed - the cap is attached to the base with only four tags. When installed, the cap is well connected to the base but when the thermostat fails there is a gap between the base and the cap. I measure it at about 0.5mm gap when they fail. At that point, the cap can be rotated a few degrees once failed.

Other brands of the device is crimped 360 around the base. My opinion is that the Derwent stat housing is cheaply designed and manufactured but sold expensive now. They used to be cheap, and if they were still cheap I would just have a box of them and swap them as they fail. $75+GST+Freight aint cheap.

Posted Friday 2 Feb 2018 @ 3:03:15 am from IP #
Bushwalker
Member

Here is one of the failed Derwent thermostats compared to another popular thermostat.

You can see the split between the cap and the base of the Derwent. When new, they have no visible gap, and no way the cap can be rotated.

The other one is popular, cheap, and crimped all around the base. It won't fail like the Derwent. No 57C version though.

Hooked the temperature controller up to switch the system at 57C so we will find out which side of the system is a problem: The thermostat on the tank or the outside compressor system.

Posted Friday 2 Feb 2018 @ 6:07:29 am from IP #
Bushwalker
Member

And the first overnight heating of the hot water tank using the electronic temp controller overnight.

Heated the water to the correct temp 57C at the midpoint in the tank.

The switch in the outside compressor didn't trip during the heating system.

Will take a few days to be sure, but looking good!

Posted Friday 2 Feb 2018 @ 9:24:30 pm from IP #
Bushwalker
Member

Three more days on the electronic thermostat, and no fail.

Looks to be solved, have now ordered a second of the same device as a backup for $20 just in case the device fails due to electricity spike etc.

Posted Monday 5 Feb 2018 @ 12:59:52 am from IP #
scott drew
Member

Good to hear.

So to clarify in my mind what you have done is;

Bought the item in the second pic in your post Posted Wednesday 31 Jan 2018 @ 8:08:24 am
Connected the item to 240v power point
Hooked one sensor wire to the tank
Hooked one control wire to the compressor
Set the item to 57 degrees C

Now it works like new?

SD

Posted Monday 5 Feb 2018 @ 4:09:16 am from IP #
Bushwalker
Member

Sort of.

Bought the item in the second pic, yes.
Connected the item to 240V, yes.
* Connected the sensor to the tank, next to the faulty stat, surrounded it with insulation.
* Connected the TWO wires from the normal thermostat to the new device. Those two wires are now connected to a 240V relay inside the new device. The other end of those existing two wires connect to the compressor controls outside.
Set the temp to 57C, yes.

Now it works like new. Yes

Posted Monday 5 Feb 2018 @ 7:34:44 am from IP #
Bushwalker
Member

Ok, the electronic thermostat device has now been working reliable 100% for more than a week.

The backup for the electronic thermostat device arrived during last week for $19.99. The backup is here in case an electricity spike etc damages the thermostat.

Let the hot water bloke who also does repairs on the Siddons, and will drop in to check it out. Agrees about the stupid cost of the standard thermostat and if he likes it he will offer the device to his other Siddons customers.

I'm now calling this a WIN!

Posted Saturday 10 Feb 2018 @ 10:36:56 pm from IP #

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