Thermia Diplomat DHP-L Outside Sensor

[Andyh747]

Hi All,

 

I need to source a replacement sensor for this heat pump.  Does anyone know what type of sensor this is and where a replacement can be obtained?  

 

Many thanks.

[SteamyTea]

19 hours ago, Andyh747 said:

Hi All,

 

I need to source a replacement sensor for this heat pump.  Does anyone know what type of sensor this is and where a replacement can be obtained?  

 

Many thanks.

Have you got a picture of it, from the inside.

It may be a cheap, off the shelf, temperature sensor.

[Andyh747]

Yes see attached. 
 

 

[ProDave]

How do you know it is the sensor that is the issue not with wiring connecting it?

 

If you carefully turn that little square black thing over see if there is any writing on the other side to identify it?

 

Do you have a multimeter?

[Andyh747]

Wiring already tested with MFT. 
The heatpump stats are constantly monitored. The outside temperature is reading 5 degrees and has been since the 8th Dec. Could be the heatpump interface but everything else is functioning. I'd like to test the sensor if possible but depends what type of sensor it is. 
 

I'll try and see if any writing on sensor. 

 

EDIT:

In addition if the sensor is disconnected from the heatpump the heatpump reports an error with the sensor and the reading goes blank.  So the sensor is providing valid connection to the heatpump but the value is not changing.  

Edited 21 hours ago by Andyh747

[ProDave]

I would take a hair dryer on an extension lead and warm it up and see if the reading changes.

 

It is just a thermistor so it's resistance will change with temperature.  If you have a plain ordinary multi meter disconnect it at the heat pump end and measure the resistance.  Then warm it up and see if that resistance changes.  If it does then it is not the sensor that is faulty.

[dpmiller]

any chance of a photo with a wider view for some context? That looks a bit like a suppression capacitor to me...

[Andyh747]

Here's front and back of sensor. That's all there is to the sensor. The casing is just protection from elements and connector block. 
 

Photos attached. 

[ProDave]

So do you have a multimeter to test it?

[Andyh747]

See above. Tested with MFT. 
 

open circuit so definitely the issue. Now just need to source replacement. Can get whole unit from Europe but would be nice to just replace the thermistor. 

[ProDave]

3 minutes ago, Andyh747 said:

See above. Tested with MFT. 
 

open circuit so definitely the issue. Now just need to source replacement. Can get whole unit from Europe but would be nice to just replace the thermistor. 

Don't trust an MFT for that, it might only have a limited resistance range, try an old fashioned simple multi meter on ohms range.

 

Or at least try your MFT with say a 100Kohm ordinary resistor to check it will read that high.

 

If it was really open circuit, your HP would display the error message that it displays when you disconnect it.

[Andyh747]

It's an MFT used for electrical testing. It goes from 0 to 999 Mohms. It's a Meggar 1741+ if you want to check the spec. Way more sensitive than a standard Multimeter. 

[ProDave]

See second part of my reply, if it is really open circuit, how come you get a temperature reading with it connected but an error code when you disconnect it?

Anyway a thermistor is marked using coloured stripes using the resistor colour code that looks to be therefore green black black gold.  So 500 plus the gold, not sure what the gold means in the context of a thermistor?

[JohnMo]

2 hours ago, Andyh747 said:

outside temperature is reading 5 degrees and has been since the 8th Dec

Have you done the simple switch off and back on again?

[Andyh747]

Quote

See second part of my reply, if it is really open circuit, how come you get a temperature reading with it connected but an error code when you disconnect it?

Anyway a thermistor is marked using coloured stripes using the resistor colour code that looks to be therefore green black black gold.  So 500 plus the gold, not sure what the gold means in the context of a thermistor?

It may have been on the way out but it’s now open circuit and heatpump shows unconnected so it’s failed completely now.

 

I think I’ll just bite the bullet and buy a complete new sensor plus housing.

[Andyh747]

Quote

Have you done the simple switch off and back on again?

See previous posts the sensor has failed.  You could switch it on/off all day but unfortunately it won’t bring a failed sensor back to life.

[ProDave]

do you have lots of fixed resistors available?  If so I would connect different values one at a time, say 1K, 10K 100K to start with.  And note the readings you get on the heat pump for each.  From that you can plot the graph of resistance vs temperature and thus determine the slope of the thermistor required and then buy one.

[Andyh747]

Thanks, great suggestion.  I have a few resistors but not enough to experiment.  I’ll source some and do some experiments. 👍

[SteamyTea]

4 hours ago, Andyh747 said:

 I have a few resistors but not enough to experiment.  I’ll source

Stick a 47k one in, always makes me raspberry pi circuits work.

 

May be worth doing an Google image search on the components.