Grill Thermocouple

[Ray]

Have received a replacement thermocouple I ordered and it arrived with warnings about only being fitted by professional accredited engineers etc.

It basically screws in at the business end with an electrical spade connection at the other. So long as I check that it does indeed stop gas flowing as designed and allows it when hot/alight surely I don't really need to get someone to fit it? 

[BroadAmbition]

I've changed ours before now and tested them mysen without any issues.  But we have a bubble tester in the system as a back up

Griff

[Guest]

Nah, you will be OK Ray. It is only gas, couldn't hurt anyone. Crack on with it 

[Popeye]

Two old sayings:

Rules are made for fools.

What the eye don't see the heart don't grieve.

Just do it. Fitting one is not rocket science and just needs a bit of common sense.

In the days that you could install your own gas central heating boiler in a house I did it myself and had it checked over by a professional and he passed it with full colours. I am still here and so is the house and the boiler is still going strong after over 30 years. There are no gas leaks and no carbon monoxide leaks. I will not let a so called "gas engineer" anywhere near it.

A member of my family had a new gas boiler installed a short time ago by a "gas engineer" and he made a complete hash of it, did not adjust the output values properly and left water leaks too. He installed the boiler and then ripped out the water pump to flush the radiator system thus invalidating the manufacturer's guarantee. A monkey could do better.

[Vaughan]

By all means go ahead if you wish.  I used to work for Jenners, so I have seen enough gas explosions on boats to know how important the "rules" are.  I am also ex CORGI so I know what the rules are for.

What exactly are you changing, on the grill?  If it just has an electric spade connection this is more probably the spark ignition, or "Piezzo" in which case, go ahead.

A so-called thermocouple comes in two parts:

1/. the probe which sits in the flame of the burner and has a thin copper pipe running up to the control button, where it screws  into the back of it with a small nut.  In which case, be very careful as the pipe is fragile.  It is actually an inner and outer cable, which passes a small current to a little solenoid in the control unit.  You are not opening a gas line by doing this, so you cannot be in danger of a gas leak.  Just make sure that the tip of the probe is positioned so that it is being fully heated by the gas flame, or it won't work.  Often, these have just been bent out of position when cleaning.  Also ensure the little fixing nut is clean and tight, as it is an electrical connection.

2/. The control unit itself, which incorporates the k n o b that you have to hold in while you are lighting the flame.  I do not recommend that you attempt to replace this yourself and I am not going to try to tell you how to do so.

3/. Why do you think you need to replace the thermocouple?  They are a very simple and sturdy affair which almost never need replacing, but might need cleaning or adjusting.  In which case you will be far better off talking to a boatyard, who do this sort of work all the time.  Peace of mind and security would only cost one hour's labour.

 

[Ray]

Thank you Vaughan, your detailed answer has made me realise that I hadn't really understood what I was looking at!

The thermocouple connects behind the kn ob with an electric style spade connection, the probe end is exactly as you describe.

Currently the **** has to be held in a very long time before the grill stays slight on it's own, I have cleaned the probe and checked it's position.

I had thought that the thin copper was just a protected wire/electric connection.

Lesson learned though, I shall have a yard look at it for peace of mind

I removed the spade connector and left it off a few days ago, as I understand it this is safe as no gas line is opened by doing this.

Thanks again 👍

[Vaughan]

It's very simple, really. The probe in the flame is bi-metallic and the action of heating the two metals creates a micro electric current which passes up to a little solenoid in the back of the gas control ****.  When you turn on the gas and hold the **** in, this lets gas through to the burner.  Once the flame has heated the probe, the current passes and holds down the gas valve, so you can then let it go.  If the flame blows out, the probe cools down, the current ceases and the solenoid lets the valve go.

When you turn off the gas, you will hear a clunk after about 20 seconds, which is the thermocouple letting go. If you don't hear this clunk, then you have a defective thermocouple.

All the same, an electric spade connection as you describe, would not be the thermocouple, but the spark ignition.  On some grills, these both function off the same control, so you just push and turn the kno b and the gas lights.

[Vaughan]

It's funny that I am allowed to say nipple but not K N O B as both are engineering terms. I wish I could think of another word for it, but I can't!

[Vaughan]

35 minutes ago, Ray said:

Currently the **** has to be held in a very long time before the grill stays slight on it's own, I have cleaned the probe and checked it's position.

In which case, either the probe is not getting hot enough, or the connection of the copper pipe at the back of the control is not passing enough current.  Unscrew the connection by the small nut and you will find a small round end in the middle, which is the electric connection, a bit like a small pin for an electric plug.  Ensure this is clean, also inside the connection itself, with a small soft wire brush.  When you put it back, ensure the nut is fully screwed in and tight.

[Mouldy]

Could be worse.  I had a warning from Facebook for mentioning Cockshoot Dyke a few weeks ago!!

[grendel]

2 hours ago, Vaughan said:

It's funny that I am allowed to say nipple but not K N O B as both are engineering terms. I wish I could think of another word for it, but I can't!

Sorry about that, it's a built in naughty word filter, created by Americans, so very much leant towards their naughty words

[grendel]

1 hour ago, Mouldy said:

Could be worse.  I had a warning from Facebook for mentioning Cockshoot Dyke a few weeks ago!!

I got away with it a few weeks back on Facebook, maybe because I put a space in the first word, and fooled their mucky word filter robots.

[Popeye]

On one of my recent posts on this forum the word filter threw out the word "p u s s e y". I wonder why?

[Meantime]

2 hours ago, Vaughan said:

All the same, an electric spade connection as you describe, would not be the thermocouple, but the spark ignition.  On some grills, these both function off the same control, so you just push and turn the kno b and the gas lights.

Some thermocouples do come with a spade connector such as the Hotpoint one below. Thermocouples are not a bi metallic strip, although you are right to suggest there are two different types of metal used in a thermocouple. When metal is heated is causes electrons to flow away from the source of the heat. Differing metals have slightly different flow rates. If you join two different metals and place this joint in a flame, known as the Hot junction, electrons will flow away from the Hot junction at differing speeds thus creating a small potential difference, voltage at the other end known as the Cold junction. This is plugged into the control solenoid and used to keep the gas valve open. Once heat is removed such as when the gas blows out the probe cools down and the voltage stops and thus the solenoid drops out cutting off the gas. 

[Mouldy]

26 minutes ago, grendel said:

Sorry about that, it's a built in naughty word filter, created by Americans, so very much leant towards their naughty words

Strange then that I can get away with Cockshoot Dyke on here!! 😉

[Ray]

So! Re-reading all of the above carefully. I would be safe to carefully replace the thermocouple as long as I only plugged the spade in at the nob end and inserted the probe and tightened the nut at the hot end as nothing I touched would be to do with the gas and pipes themselves?

(The utter confusion the above may cause the filter was unintentional)

[Meantime]

3 minutes ago, Ray said:

So! Re-reading all of the above carefully. I would be safe to carefully replace the thermocouple as long as I only plugged the spade in at the nob end and inserted the probe and tightened the nut at the hot end as nothing I touched would be to do with the gas and pipes themselves?

(The utter confusion the above may cause the filter was unintentional)

In theory yes because you are only working on low voltage electrical connections. It is also a fail safe device so if you fit it incorrectly you'll have the problem of it not staying alight.

I say in theory because to access and change the thermocouple there is the slight possibility of disturbing a gas joint unintentionally. If you have a bubble gas leak detector as part of your gas installation then it should be easy to check for unintentional leaks. As long as your very careful around any gas joints then you should be fine.

[Meantime]

For reference, this is the more usual style of thermocouple with a nut on the cold junction end, that could look like it is a gas style connection, again though it is only an electrical connection and can be disturbed and replaced without breaking any gas seals.

[FairTmiddlin]

52 minutes ago, Meantime said:

For reference, this is the more usual style of thermocouple with a nut on the cold junction end, that could look like it is a gas style connection, again though it is only an electrical connection and can be disturbed and replaced without breaking any gas seals.

Sorry Meantime it is not an Electrical connection. It's a Magnetic switch The heat on the tip causes two different metals to creates an Electro Magnetic Field which activates the solenoid to keep the gas flowing.

[Meantime]

7 minutes ago, FairTmiddlin said:

Sorry Meantime it is not an Electrical connection. It's a Magnetic switch The heat on the tip causes two different metals to creates an Electro Magnetic Field which activates the solenoid to keep the gas flowing.

I beg to differ. The voltage created by the thermocouple will cause a solenoid to engage at the cold junction end and it is this that you will hear click as it disengages about 20 seconds after the flame has gone out, but it is most definitely operated by voltage induced as a result of using two differing types of metal in the thermocouple. 

For a fuller description it is worth reading here

[Vaughan]

I think we all get the point, don't we? Which, in answer to the OP's question, is that checking and servicing the probe and pipework for the thermocouple does not involve opening a gas line and is therefore not dangerous to attempt one's self.

 

[ChrisB]

You live and learn. I never knew bi-metalic strips were used produce a small current.

We used Brass/Invar 36 bi-metalic in the chemical industry to covert heat into mechanical movement for cut-outs in low flash areas.

[Smoggy]

Thermocouples are not a bi-metallic strip that works by different expansion rates, they are just a welded junction of two different metals, that said a bi-metallic strip is likely to produce a small voltage too if hot enough but the range will be determined by the metals used, the voltage produced by a type k thermocouple is only in the millivolt range.

 

[Meantime]

15 minutes ago, Smoggy said:

Thermocouples are not a bi-metallic strip that works by different expansion rates, they are just a welded junction of two different metals, that said a bi-metallic strip is likely to produce a small voltage too if hot enough but the range will be determined by the metals used, the voltage produced by a type k thermocouple is only in the millivolt range.

 

Indeed it is the presence of two differing metals that often causes the confusion. The Seebeck effect describes the way in which electrons are caused to move down a conductor when it is warmer at one end than the other. Where there is a temperature gradient along the conductor. Whilst this creates a voltage, if two wires of the same metal are used then the voltage at the opposite ends is the same and since a potential difference doesn't exist no voltage can be measured and there is no voltage difference to operate a solenoid. By using two different metals the voltages generated are different and thus a potential difference exists at the cold junction end which is enough to operate a small solenoid.

[FairTmiddlin]

2 hours ago, Meantime said:

I beg to differ. The voltage created by the thermocouple will cause a solenoid to engage at the cold junction end and it is this that you will hear click as it disengages about 20 seconds after the flame has gone out, but it is most definitely operated by voltage induced as a result of using two differing types of metal in the thermocouple. 

 

Differs from my Propane Butane CORGI training then.