# solar pump not cutting out



## villa 1 (12 Jun 2013)

Hi Folks. This a question for all the solar wizzes out there
Since the end of the warm weather last week my pump on the solar installation is refusing to turn off, even at night.
I'm just wondering is this down to a faulty sensor or faulty controller. I have taken out the lower sensor to see if is working( partially immersing in warm water) and this cuts out the pump. When I insert the sensor back into the probe in the cylinder the pump turns on and will not turn off.
I have checked for reversed circulation and this is not happening.
I have also checked the settings on the controller and they match the factory settings.
I am now having to manually turn off the controller by night, but this will be overridden after eight hours and the pump turns back on.
There is very little heat generation at the moment due to cloudy weather but I don't like the idea of a pump running continuously preferring it to cycle on and off which was the norm up until the weekend
The system has worked very well since it was installed three years ago(new house, two flat plates, potterton controller).
I have contacted the plumbing contractor who done the install but he is not getting back to me with any solutions.
Any Ideas?
Any Ideas


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## Shane007 (12 Jun 2013)

It sounds like a faulty sensor.
What is the reading on both T1 & T2?
The controller is just a temperature differential controller, i.e. works by switching on & off the pump based on the temperature difference between T1 on the roof & T2 at the bottom of the cylinder. Usually switches on when there is an 8C difference & off when there is a 4C difference but this can be changed within the controller.
If you have a multi-meter you can take a resistance reading from the sensor. They are just a basic NTC Thermistor.
Readings should be generally as follows:
10C 1039 ohms
20C 1078 ohms
30C 1117 ohms
40C 1155 ohms
50C 1194 ohms

They are a very cheap replacement part, approx €10 - €15. They are called PT1000 sensors.
I would be more looking at T1 on the roof as being faulty. See what the temperature reading is right now. Mine is reading 15C @ 9.30pm now.


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## villa 1 (13 Jun 2013)

Thanks for your input Shane 

11.45 now and the roof panel sensor is at 15deg. Pump has not come on as of yet. Was running last night and had to do a manual shut off on controller. Will keep you posted.


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## Shane007 (13 Jun 2013)

15C on roof & pump off. All ok but if it happens again, take note of the temperatures of T1 & T2 whilst the pump is running when it shouldn't be. Then you should see an abnormal reading of the sensor if faulty.
I had a call out once where the roof sensor was reading 1400C at night! Pump would therefore never switch off as there would never be only a 4C difference between T1 & T2.


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## villa 1 (13 Jun 2013)

9.30am T1 panel 33deg, T2 tank bottom 25deg, sunny at the moment, pump on, well see how it goes.
Keep you posted, thanks


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## Shane007 (21 Jun 2013)

Hi Villa1,
Did the issue resolve itself?


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## villa 1 (21 Jun 2013)

Hi Shane.
All was working quite nicely with plenty of heat in cyl. and pump cutting off as it should be. Came home last night at 11.45, low and behold pump was circulating. I did a manual shut off and that stopped that. 
Pump has kicked in this morning(as the sun is out) so I'll keep an eye on things tonight. This is little confusing as since the initial problem things settled down with no nigh-time pump activity. Any ideas?
Thanks for your interest and i'll keep you posted.


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## Shane007 (21 Jun 2013)

What was the temperature readings on T1 & T2 last night when the pump was running?


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## quentingargan (22 Jun 2013)

Just wondering - are you sure your system isn't on HOLIDAY mode? This causes the pump to run at night to cool the cylinder...


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## Shane007 (22 Jun 2013)

quentingargan said:


> Just wondering - are you sure your system isn't on HOLIDAY mode? This causes the pump to run at night to cool the cylinder...



I thought of that initially but then it would be happening every night.


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## quentingargan (22 Jun 2013)

Shane007 said:


> I thought of that initially but then it would be happening every night.


Depends on whether some hot water is used, or whether the probe is at the bottom of the cylinder. If you use hot water immediately after sundown and lower the temperature at the bottom of the cylinder, the pump may not then kick in, or may kick in sporadically. I think you are probably right, but it is worth looking at.


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## villa 1 (22 Jun 2013)

Hi Lads.

I'm not sure if there is a holiday mode in the Potterton controller but this problem seems to sporadic.
When the pump is running at night it is not guaranteed that the cylinder has been heated to it's full capacity. This form of heat dumping seems to transfer only a small (if any) amount of heat into the panels. I have checked the flow/return pipework and there is very little in the way of heat transfer occurring.
As the cold feed to the cylinder is near the solar coil it seems likely that the cooler water entering should activate shut off on the solar pump especially when hot water id drawn off. I'll keep an eye on things, good idea to have a holiday mode in the controller if it is in place.
Regards, V


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