Electric oil radiator not switching off when desired temperature reached

Thread Starter

Steve90

Joined Oct 18, 2020
13
Hello all,

I need some help with an electric oil filled radiator that’s developed a problem.

Basically the heating function is on all the time!

By that I mean once it’s reached the desired temperature (set on the front LED display) instead of the heating function stopping it just carries on heating the oil. The only way to stop it is to power the unit off, which we are doing via the remote so we don’t have to keep getting up.

The heater has been in storage so the warranty has unfortunately now run out. But it’s been used just a handful of times so is practically brand new and I’m hoping easy to fix.

I have opened up the unit and uploaded some photos of the circuit board.

One of the photos has something that looks like a thermistor, which I believe can be used as a temperature sensor so I’m wondering if it could be that that’s causing the problem?

If it is that and they come in different types and specifications can anyone please advise which one I should get?

Or is the problem more complicated than just changing the thermistor?

Your help would be much appreciated.

Thanks

Steve
 

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MrChips

Joined Oct 2, 2009
22,107
We would be interested in seeing more detail on the lower-left half of the board beside those two black boxes (relays). Why are there two relays? Why is there Heat1 and Heat2?

What LEDs are on before and after target temperature is reached?

Do you have a test meter (DMM = digital multi-meter)?
 

AlbertHall

Joined Jun 4, 2014
10,572
Do you have a multimeter with ohms ranges?
If so measure the resistance across the terminals of the thermistor connector where it connects to the circuit board, and note the reading.
Then unplug the thermistor from the connector and check the same resistance reading. It should be higher than the first reading. If it is then the thermistor is connected to the board and is probably OK.
 

Dodgydave

Joined Jun 22, 2012
9,686
If it's a Ntc type then as it gets warmer the resistance will go lower and vice versa, as said measure the resistance unplugged and note it, then heat it up with your hand or a flame and it should change in resistance.
 

AlbertHall

Joined Jun 4, 2014
10,572
If it's a Ntc type then as it gets warmer the resistance will go lower and vice versa, as said measure the resistance unplugged and note it, then heat it up with your hand or a flame and it should change in resistance.
I should steer clear of a flame if I were you.
 

Thread Starter

Steve90

Joined Oct 18, 2020
13
@MrChips:
-- I will take a closer pic of the two black boxes on the lower-half tomorrow and upload.
-- Don't know why there are 2 relays, and why there is a Heat1 and Heat2.
-- The LEDS that are on before and after the desired temperature is reached are the same, there is no difference.
That is on the right the bottom Power LED and top Centigrade LED are always ON, and the middle Timed LED is
only ON when the timer function is used. On the left only one LED is On depending on whether Low, Med or High
Heat setting is selected.
-- There is an LED that is right next to the High LED which flashes on and off all the time ie before or after the desired
temperature is reached , and I have no idea why it does this.
-- I do actually have a User Manual for the heater in PDF format that I could upload if that will help?


As for a multimeter with ohms range , yes I do have one and will test the thermistor at the terminals as suggested by all.

By the way I found when I disconnect the thermistor from the terminal block and power the unit up, the LED Display instead of showing a temperature shows the code "E2". I presume this is just an error code that comes up if it doesn't detect a thermistor connected?
 

MrChips

Joined Oct 2, 2009
22,107
If the controller is reaching the set temperature I would assume that the thermistor is working.

The problem is between the relay driver and the relay.
If you have a DMM I was going to suggest where you can test to try and narrow down where the fault lies.
The first test would be to look at the voltages on the relay coils. But before we do that it would be nice to see what is connected to Heat1 and Heat2.

Maybe the relay contacts have welded closed and the relay needs replacing.
 

Thread Starter

Steve90

Joined Oct 18, 2020
13
I have a digital room thermometer and if I set the desired temperature to be at it's lowest setting for this heater ie 15 degree Centigrade and the digital thermometer is showing the room to be over 20 degrees Centigrade, the heater frustratingly still comes on... and stays on... continuing to warm the room even higher!

So by controller if you mean the temperature controller then surely it can't be working properly if the desired temperature set on the LED Display is much lower than the room temperature yet it still comes on when it shouldn't.

If it's not the thermistor then may be it is one of the relays. I don't know how these things are designed and what circuitry controls what. But there must be a temperature senser/controller component which then must control the heating coming on and off.

As mentioned the unit is barely used so it can't be any component that has past it's life span.
 

MrChips

Joined Oct 2, 2009
22,107
I have a digital room thermometer and if I set the desired temperature to be at it's lowest setting for this heater ie 15 degree Centigrade and the digital thermometer is showing the room to be over 20 degrees Centigrade, the heater frustratingly still comes on... and stays on... continuing to warm the room even higher!
Does the unit show correct room temperature? If it does not, then the problem lies with the temperature measuring portion which includes the thermistor.

As mentioned the unit is barely used so it can't be any component that has past it's life span.
That does not follow. A component can go bad at any time in its expected life span. The probability of it going bad at a certain age is a different issue.
 

Thread Starter

Steve90

Joined Oct 18, 2020
13
Good points about the unit possibly not displaying the correct room temperature and also yes components can go anytime! :)

By the way (and sorry for the dumb question!) but how does one include in a reply all or part of someone's previous reply?... haven't quite worked that out.

Anyway, I managed to test the thermistor with a multimeter. I set the multimeter to 20k ohms and at room temperature the thermistor read around 9.95 on the meter. I then safely and slowly warmed the "bead" end of the thermistor and saw the reading drop from 9.95 down to 2.05. Once it had cooled to room temperature again the reading went back up to around 9.95. I guess this demonstrates the thermistor is working fine?

@MrChips... You were interested in a close up of the relays and where the relay wiring goes. I have uploaded three more pics which should help with this.

The heater has a 2.5kw output rating, with 3 heat settings 1kW, 1.5kw and 2.5kw. Looking at the wiring of the Heating Element at the bottom of the radiator fin it looks like there are 2 heating elements labelled "I" and "II". One relay is connected to heating element "I", and the other relay is connected to heating element "II".

I think when either the Low or Med heat setting is chosen on the controls, only one relay and therefore only one heating element is being unitlised (ie for either 1kw or 1.5kw output). However if the heat setting on the control is set to High then both relays are in operation , utilising both heating elements on the radiator (ie for max 2.5kw output).

I'm not sure how one tests theses relays but since the thermistor seems fine and these Relays are very low cost, should I just go ahead and swap them out for two new ones?

I do appreciation everyone's assistance with this problem. The radiator was not cheap when purchased (though it's come down in price now) and I hate to throw it out but as it stands it can't be used unmonitored as the heating doesn't switch off.
 

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AlbertHall

Joined Jun 4, 2014
10,572
Looking at the middle picture, Unplug the H1 and H2 wires then check the resistance between the L connector and each of the H1 and H2 connectors on the board.
With the power off both relays should be in the open state so there should be no connection shown in those resistance readings on the highest resistance range.
If that is OK, then the relay contacts are not welded.
 

Alec_t

Joined Sep 17, 2013
11,752
If it's not the thermistor then may be it is one of the relays. I don't know how these things are designed and what circuitry controls what.
My guess is that one relay switches a heater element of xkW rating and the other switches a heater element of ykW rating, so one or both elements on would give you the Low, Medium and High modes. Does the mode setting make any difference to whether the heater stays on or not?
 
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Thread Starter

Steve90

Joined Oct 18, 2020
13
No the mode setting makes no difference to whether the heater stays on or not.

Will test the relays as was suggested by AlbertHall but I'm wondering if the fault always existed with this unit.

We bought it as a back up in case the boiler broke down and it was hardly used at all. We've now downsized into flat which has no gas just electric, and the EPC report highlighted that the electric wall heaters were not very efficient. Hence we thought we would start using this oil radiator, and it's only now that we've noticed it just stays on all the time. So it's possible the problem existed from when it was first bought. could it be a faulty board?

We can still use the oil radiator, it just needs to be turned off manually by us when the room gets too warm, but this gets annoyig after a while.

I might be flogging a dead horse here... instead of spending all this time on it maybe I should just go buy another:rolleyes:
 

Thread Starter

Steve90

Joined Oct 18, 2020
13
If we can't fix it you could plug it into one of these.
That was actually suggested to me by a work colleague, but there's a really dumb design aspect to this unit. When you power the unit from the mains (ie switch the power On-to-Off then Off-to-On via mains plag) the unit comes up in Standby Mode!... to then you have to press either the "On/Off" button on the Unit's front panel or on the remote to switch it on!... so sadly can't use one of these smart plugs.
 

MrChips

Joined Oct 2, 2009
22,107
I would replace the relays only if I am sure the problem is in the relays.

Did you confirm that the unit is displaying the correct room temperature?

As Dodgydave suggests, measure the voltage across the relay coil when the heater is supposed to be on and when it is supposed to be off.
 

scorbin1

Joined Dec 24, 2019
45
When you say the heating is not turning off, what exactly is giving you the idea that it is not turning off? Does the temperature continue to climb significantly after it reaches the desired temperature? Does the readout indicate much higher temperature than desired? I ask because a lot of heaters use a PID controller. These controllers learn over time and adjust their control parameters to reduce temperature oscillations due to the hysteresis of the control circuit. Reaching the desired temperature does not turn off the elements, but rather, it usually modulates them to reduce heating gradually. This helps to reach a steady state much faster and more efficiently.

The relays seem to suggest it isn't actually modulating the power level as I suggested (for ex. with PWM), but rather it does so using asymmetrical elements and those relays. This could be an indication of a somewhat crude implementation of a PID loop. I wonder if it is also trying to emulate other portions of a PID loop by keeping the element(s) powered for some, non-constant, duration after setpoint is reached and also powering up the element(s) sooner than reaching the lower limit.

Just a thought.
 
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