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Dometic RM5310 fridge problem


blackrose

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On 16/07/2017 at 11:45, Stormbringer said:

Your fridge would be iced up and food on the top shelf would probably start to freeze. If unsure I would monitor the fridge with a clamp meter ..they pull about half an amp @ 240 v 

The place that sold me the new element suggested putting the fridge on full cooling for a couple of hours with everything else on the boat switched off, and then turning the adjustment down to minimum. I should be able to see if the thermostat is working by looking at my mains Owl monitor.

On 16/07/2017 at 10:28, mross said:

How many wires are there?  The photo is blurred.  If you look at fig 14 on page 11 of the INSTALLATION manual, the AC heater is item 11.  You need to measure across the two, brown wires.  

Two brown, one earth

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27 minutes ago, blackrose said:

The place that sold me the new element suggested putting the fridge on full cooling for a couple of hours with everything else on the boat switched off, and then turning the adjustment down to minimum. I should be able to see if the thermostat is working by looking at my mains Owl monitor.

Two brown, one earth

That will work...I have a modified hook up lead with the live available for a clamp meter...very handy 

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I've replaced the mains element and the fridge is working from mains now. Tested the thermostat and it's working. So at least I've got a fridge while I'm on shore power.

On gas, I replaced the gas jet but that hasn't solved the problem of it cutting out. It basically runs on the high flame but as soon as it gets up (down?) to temperature and tries to reduce the flame it cuts out. Could it be the thermocouple or something else? 

Edited by blackrose
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41 minutes ago, blackrose said:

On gas, I replaced the gas jet but that hasn't solved the problem of it cutting out. It basically runs on the high flame but as soon as it gets up (down?) to temperature and tries to reduce the flame it cuts out. Could it be the thermocouple or something else? 

It could very well be the thermocouple. Or possibly more likely, the position of the thermocouple. Is it still in the flame when the flame reduces in size?

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6 minutes ago, WotEver said:

It could very well be the thermocouple. Or possibly more likely, the position of the thermocouple. Is it still in the flame when the flame reduces in size?

Well it's difficult to know because I never see the reduced flame, but I have moved it a couple of times and retested and nothing seems to work.

This is what the caravan place who sold me the mains element and gas jet have said:

 

I would'nt think it was the thermocouple because that is a flame failure device which turns off the gas supply if the flame goes out. The thermocouple may actually be turning the gas off because the flame is going too low to keep the thermocouple tip hot. but that just proves it is working and not faulty.

It is very difficult to diagnose a fault without actually seeing it but:

1) I assume you made sure the burner assembly was completely cleaned out when you changed the jet!!!! I also assume that there is no problem with the flame for a while when the fridge is first lit.

If so then:-

2) Make sure the thermocouple tip is correctly positioned into the flame because if not it will cool down on the lower flame and do as it should which is to turn off the gas.

When you are sure this is right if there is still a problem:-

3) I would now look at the thermostat as it is the thermostat which regulates the gas supply when the fridge cooling plates are cold enough and this could be turning the gas down too low.

Hope this helps

 
Edited by blackrose
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Hmm... they start off saying that they doubt it's the thermocouple and then go on to explain how it could be the thermocouple. 

They're only a couple of quid to replace so I'd give it a shot. Before doing that I'd run the fridge on gas with the stat set to the warmest setting and watch the flame intently so as to see exactly what happens when it reduces in size. 

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The fridge has been running on mains for a day now but when I try to switch to gas it goes out as soon as I release my finger from the temperature adjustment knob which needs to be kept depressed while lighting on gas. This is because the fridge is already up to temperature from the mains and won't stay alight on the low flame. If I let the fridge boiler cool down it will stay alight on the high flame. 

If the fridge works on the high flame but not on the low flame then presumably the thermocouple is working? I'm pretty sure the burner is clean and the thermocouple is in the correct position, so now I want to focus on the thermostat. Does anyone know how to remove/replace it?

Edited by blackrose
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43 minutes ago, blackrose said:

The fridge has been running on mains for a day now but when I try to switch to gas it goes out as soon as I release my finger from the temperature adjustment knob which needs to be kept depressed while lighting on gas. This is because the fridge is already up to temperature from the mains and won't stay alight on the low flame. If I let the fridge boiler cool down it will stay alight on the high flame. 

If the fridge works on the high flame but not on the low flame then presumably the thermocouple is working? I'm pretty sure the burner is clean and the thermocouple is in the correct position, so now I want to focus on the thermostat. Does anyone know how to remove/replace it?

Sounds to me like the thermocouple is working, but not correctly positioned. On high flame, the flame covers the thermocouple,  hence it works, but on low flame, the thermocouple is probably just out of the flame and hence it does its job and cuts the gas off. 

Try looking at the flame pattern when on low flame,  and then try moving the end of the thermocouple so that it is always bathed in flame, on high or low gas.

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1 hour ago, cuthound said:

Sounds to me like the thermocouple is working, but not correctly positioned. On high flame, the flame covers the thermocouple,  hence it works, but on low flame, the thermocouple is probably just out of the flame and hence it does its job and cuts the gas off. 

Try looking at the flame pattern when on low flame,  and then try moving the end of the thermocouple so that it is always bathed in flame, on high or low gas.

Yup, that's exactly what I was trying to say. The thermostat is obviously working (it lowers the flame) but the thermocouple is turning the fridge off. 

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1 hour ago, cuthound said:

Sounds to me like the thermocouple is working, but not correctly positioned. On high flame, the flame covers the thermocouple,  hence it works, but on low flame, the thermocouple is probably just out of the flame and hence it does its job and cuts the gas off. 

Try looking at the flame pattern when on low flame,  and then try moving the end of the thermocouple so that it is always bathed in flame, on high or low gas.

Thats' the problem - I can't look at the flame pattern on low flame because I never get a low flame - it just goes out. I've moved the thermocouple around and lowered it but it still doesn't work. Could it be an incorrectly calibrated thermocouple?

Edited by blackrose
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27 minutes ago, blackrose said:

Could it be an incorrectly calibrated thermocouple?

No,  they usually either work or they don't. 

Try experimenting with various positions, so that the tip is near the lower half of the high flame.

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Its a question of how fast it goes out. If instantly then I doubt its the thermocouple because it will still be hot from high flame, if over a few seconds then probably thermocouple related.

I seem to recall gas thermostats have a bypass "jet" to sustain the low flame, maybe this is blocked.

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Thanks. I replaced the main gas jet yesterday - I'm not sure if thee's another bypass jet - I don't think so?

The flame goes out instantly so that would suggest it's not the thermocouple.

Why is boat/caravan stuff so crap? In the last 9 months I've had to fix a relatively new water pump which was sucking in air, replace all the seals on my toilet, the fridge and I've just realised that my rarely used gas water heater isn't working!

Edited by blackrose
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Is the thermostat something that's easy to access? Presumably it has a gas pipe entering and leaving it as well as electrical connections? I'm just picking up on Tony's point and wondering if it can be cleaned (if it has the gas passing through it)?

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I can't answer either question because I have never had such a modern gas fridge apart.

On some gas fridges we had on the fleet (late 60s) there was what looked like a cigarette filter in the gas inlet connection. I assume this was to filter the gas and stop any particles that might block the gas flow. We found they did block with dust and sometimes by the liquor that collected in the bottom of the gas bottles. That would be what I looked at first.

If you can get at the inlet and outlet of the gas thermostat it might be worth trying something like an air duster to blow through backwards with the control set to off/defrost/or the warmest setting so the main vale will be closed. Try to seal the plastic air duster tube into the outlet port so you get maximum pressure. I do not hold out much hope though. I have a feeling the bypass "jet/port", if there is one, may be under a small brass hexagon accessed from the outside of the thermostat. Beware this could all be complete ollox.

This involves working on the gas system so I am not recommending that the OP tries any of this, especially as I have an idea this may be a live-a-board situation so Gassafe qualifications might be needed. (back covering on my part)..

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7 hours ago, WotEver said:

Is the thermostat something that's easy to access? Presumably it has a gas pipe entering and leaving it as well as electrical connections? I'm just picking up on Tony's point and wondering if it can be cleaned (if it has the gas passing through it)?

The thermostat is on the right of this component. The silver disc with the mini silver "pipe" running from it. A new unit is about £138.

IMG_20170723_130249.jpg

Edited by blackrose
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48 minutes ago, blackrose said:

The thermostat is on the right of this component. The silver disc with the mini silver "pipe" running from it. A new unit is about £138.

IMG_20170723_130249.jpg

The suspect gubbins would be inside the brass thingy I suspect. The silver tube is the temp sensor for the stat and we know that works because it's fine on mains. The brass valve is where I believe the stat controls the flame from high to low. Not sure what you could do about that - what do the suppliers say?

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9 minutes ago, WotEver said:

The suspect gubbins would be inside the brass thingy I suspect. The silver tube is the temp sensor for the stat and we know that works because it's fine on mains. The brass valve is where I believe the stat controls the flame from high to low. Not sure what you could do about that - what do the suppliers say?

They helped me to check the selector switch yesterday by telling me how to bridge the switch. The switch is working fine so they say it's either the thermostat or the thermocouple. As we've sort of ruled out the thermocouple it must be the stat. They told me to check everything else again as a new one is going to cost £138.

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Just now, blackrose said:

They helped me to check the selector switch yesterday by telling me how to bridge the switch. The switch is working fine so they say it's either the thermostat or the thermocouple. As we've sort of ruled out the thermocouple it must be the stat. They told me to check everything else again as a new one is going to cost £138.

Ahh, no suggestions on how to service the stat then. Shame, that. 

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