Overheating Dimplex Quantum storage heater

[phatboy]

I was unsure if I should post here, or in appliances.

I have a Quantum QM150 storage heater that's almost 10 years old, and has started overheating, the front panel measured over 60 degrees a few days ago compared to the others being mid-20s.

Dimplex will send an out of warranty engineer (The 10 year warranty is actually 5, except for rust), but I'd rather have a go myself.

I've opened it all up, checked and everything is quite clean (It was moved 18 months ago so disassembled and cleaned then). I have confirmed the fan is working, and the front insulation panel was properly in place and secured. The control panel shows no errors. No components look damaged, but I don't know what the expected resistance on cutouts would be to check them.

Where do I go from here? I was surprised a 'modern' heater could overheat, I assumed it would stop heating if a problem was detected. I cannot find a service manual anywhere for a Dimplex Quantum QM150.

Any advice welcome.

 

[EFLImpudence]

Dimplex QM150 user manual (English - 40 pages)

Manual Dimplex QM150. Access the Dimplex QM150 manual freely or pose your question to fellow Dimplex QM150 owners.

www.manuals.co.uk

 

[EFLImpudence]

Google Search

 

[phatboy]

Dimplex QM150 user manual (English - 40 pages)

Manual Dimplex QM150. Access the Dimplex QM150 manual freely or pose your question to fellow Dimplex QM150 owners.

www.manuals.co.uk

Thanks, but I need a repair or service manual

 

[phatboy]

Google Search

I am familiar with Google, thanks.

Dimplex confirmed it shouldn’t get that hot, and it never has done nearly 10 years

 

[Echo the husky]

Perhaps there is a faulty temperature sensor or a triac controlling the elements has failed short circuit. I've installed loads of these but not had any fail yet to need to do any fault finding.

 

[phatboy]

Perhaps there is a faulty temperature sensor or a triac controlling the elements has failed short circuit. I've installed loads of these but not had any fail yet to need to do any fault finding.

Excuse my stupidity, but which are the temp sensors? I believe there may be one in the insulation along the bottom. I think the 2 devices in series on the left end are thermal cutouts? 1 seems to have a reset. At the bottom of the left is a something, which has 2 wires and I cannot identify.

TRIAC issues sounds like a new circuit board would be required, and thats not cheap?

I've repaired loads of appliances (Including older XLS storage heaters), but usually with a guide and all has been well, just there are no guides or tech manuals seemingly available for these heaters.

 

[Echo the husky]

IIRC the tmp sensors are marked on the PCB, they are connected with small 2 pin connectors, a white one and a black one.

The room temperature sensor is marked below:

There are guides online how to test temperature sensors, and the expected readings for the current temperature, I would expect a fully broken, disconnected or short circuit thermistor to bring up a thermistor error code on the display.

There are 2 bi-metallic thermostats on the left side. The one at the back should trip if the unit seriously overheats, requiring manual reset. The front is a control stat and should go open circuit around the temperature stamped/printed on it, closing again as it cools down.

It is possible to test the triacs but replacing them should be left to an expert. The official repair (and one I'd recommend for DIY) would be replacing the PCB as a single unit. Dimplex call it a charge controller. It isn't too expensive, if one is required make sure you get the matching part as there have been quite a few revisions.

These heaters are a lot better designed and built than the earlier 'Duo Heat' storage heaters, (That are thankfully discontinued) I've repaired dozens of those. The circuit boards were in my opinion very poorly designed and the PCBs appeared to be designed to have a very short life, with components driven very hard.

The manual posted above is for a different revision of the QM150
Here are a load of older models of the installation manual they all have the internal wiring diagram showing all the components. I checked a few and Series D and Series G look closer to what you have. But you will have to carefully compare them/ check any internal / external labels marked with the series letter. Older Dimplex heaters had the series revision clearly marked on the top of the heater.

 

[phatboy]

IIRC the tmp sensors are marked on the PCB, they are connected with small 2 pin connectors, a white one and a black one.

The room temperature sensor is marked below:

View attachment 411316

There are guides online how to test temperature sensors, and the expected readings for the current temperature, I would expect a fully broken, disconnected or short circuit thermistor to bring up a thermistor error code on the display.

There are 2 bi-metallic thermostats on the left side. The one at the back should trip if the unit seriously overheats, requiring manual reset. The front is a control stat and should go open circuit around the temperature stamped/printed on it, closing again as it cools down.

It is possible to test the triacs but replacing them should be left to an expert. The official repair (and one I'd recommend for DIY) would be replacing the PCB as a single unit. Dimplex call it a charge controller. It isn't too expensive, if one is required make sure you get the matching part as there have been quite a few revisions.

These heaters are a lot better designed and built than the earlier 'Duo Heat' storage heaters, (That are thankfully discontinued) I've repaired dozens of those. The circuit boards were in my opinion very poorly designed and the PCBs appeared to be designed to have a very short life, with components driven very hard.

The manual posted above is for a different revision of the QM150
Here are a load of older models of the installation manual they all have the internal wiring diagram showing all the components. I checked a few and Series D and Series G look closer to what you have. But you will have to carefully compare them/ check any internal / external labels marked with the series letter. Older Dimplex heaters had the series revision clearly marked on the top of the heater.

Thank you, this is of great help!

It's a Series G, and I found the correct manual via your link - https://www.manualslib.com/manual/2351616/Dimplex-Qm050.html?page=16#manual

The bi-metallic thermostats on the left show open circuit, which I would expect.

The room temp reads as between 11.9-13.2k, over a minute or so
The core temp reads as between 93-120k, but then in the next test 110-150k

I think, with some degree of uncertainty, that these are roughly what should be expected in a room of 19 degrees. And the heater is completely cold having been off for 5 days with the insulation removed.

As for testing TRIACS, I only see 1 marked TH7 on the board. Unsure how best to test this and understand the results.

The 2 control stats (marked lower left stat, and right stat) read open circuit, but they seem to be wired only to the boost element and the fan so I don't think they are to blame.

Tim

 

[phatboy]

More research says if the charge controller needs replacing, so does the user interface so the software matches. Disappointing, and £170 or thereabouts.

 

[Echo the husky]

The sensor measurements should be fairly stable, need to be measured while disconnected from the circuit board, make sure your fingers aren't touching the meter probes as your skin resistance will skew the readings. If both sensors are at the same temperature the readings should be the same too. There is a staggering difference between 11.9K and 150K.

Carefully test the sensors again, The room temp sensor appears to be giving a sensible value for a standard 10K thermistor which is a very common type (10K at 25C). If the core sensor is still wildly off the reading of the room sensor after testing it again it should be replaced.