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Tacet

Boiler relay

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A domestic, oil-fired boiler question, please.  This relay burnt-out last week; it is a Finder 230V 8A.  The coil is energised by the call for heating from a Honeywell programmer - and the contacts then make between a permanent live and the heating PCB;  A second throw also brings in a further relay - to operate the circulation pump and burner via the same permanent live.   It is a double pole relay - but the contacts that are closed when the solenoid is not energised are unusued.  So not a great load on the burnt out relay which is rated at 8A.   Diagram attached too.  It is Relay 3 that is giving the problem

 

The relay was a few years old - so it was replaced and then worked for a day or so before it too burned out.  After a second replacement burnt out immediately, I noticed that the scorched part is, on all three, at the coil end.  Also, (temporarily) replacing the relay with a a hard wired switch makes the boiler operate fine - albeit flat out or nothing.

 

It all seemed a bit odd - so on fitting the third replacement, I removed the supply and load across the switched contacts and .... it burnt out immediately taking out a 5A cartridge fuse on the fused spur and a 6A MCB on the consumer unit.

 

I have taken the relay carrier apart in case something very strange was happening, and it looks OK (another is on order) with some slight scorching.  Now suspecting the output from the programmer receiver (it is a wireless timer/room stat) - but only with a simple multimeter, it reads about 245V which is only a little over the printed 230V and the specification suggests it is OK up to 400V.  I have checked all replacement relays are rated at 230V and they have been sourced from two (soon to be three) suppliers.

 

This is proving a bit expensive at £6 a bang, and as the boiler is outside, even ensuing heat is wasted.

 

Any suggestions will be appreciated.

 

Finder relay.jpg

Wiring diagram 2.jpg

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40 minutes ago, Tacet said:

I have taken the relay carrier apart in case something very strange was happening, and it looks OK (another is on order) with some slight scorching.  Now suspecting the output from the programmer receiver (it is a wireless timer/room stat) - but only with a simple multimeter, it reads about 245V which is only a little over the printed 230V and the specification suggests it is OK up to 400V.  I have checked all replacement relays are rated at 230V and they have been sourced from two (soon to be three) suppliers.

 

 

 

Most curious. 

 

Given you have proved it is the relay actuating coil blowing the 5a fuse I suspect what you are actually being supplied with is wrongly labelled 12v relays. Invest in a few more but before you plug in the next one, use your multimeter to measure the coil resistance. I'd be expecting something well over 5kOhms, possibly as high as 50kOhms. If you get something around 50 Ohms or lower, then you have a wrongly identified relay, probably 12v.  

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8 minutes ago, Mike the Boilerman said:

 

 

Most curious. 

 

Given you have proved it is the relay actuating coil blowing the 5a fuse I suspect what you are actually being supplied with is wrongly labelled 12v relays. Invest in a few more but before you plug in the next one, use your multimeter to measure the coil resistance. I'd be expecting something well over 5kOhms, possibly as high as 50kOhms. If you get something around 50 Ohms or lower, then you have a wrongly identified relay, probably 12v.  

Mike

 

Thanks for that.  Having suspect electrical skills, I have been ordering one relay a day to replace the one that I burn out.  So the supply line is  running well - and when this is finally fixed, I ought to have one or two spare relays still to arrive.

 

I'll check the resistance of a new one tomorrow.  Having been supplied by two separate firms (should be three by tomorrow), it would be odd if they were labelled incorrectly.  But it is possible.  On the same lines, I might try the next relay well away from the boiler  first - and if that's ok, connect up the switched contacts to the boiler etc - but actuate the relay from a separate supply (via an open window!).  If it works, it ought to point the finger towards the switched live coming from the programmer receiver.  There are COMPONENTS (oh err) in the receiver box - presumably, it is just possible that it is dishing out an unsatisfactory switched live or is that beyond all reason?

 

Of course, the most probable cause is that I have done something monumentally stupid,  I did have to play around to trace the issue at the beginning - but don't know what I might have done.  I could call someone out.  Last time I had an issue - a oil boiler technician attended.  He was genuinely helpful insofar as we talked it through- but ultimately did not know much more than me - which is not much.  After he had gone, I traced it to a duff PCB.

 

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1 hour ago, Tacet said:

The relay was a few years old - so it was replaced and then worked for a day or so before it too burned out.  After a second replacement burnt out immediately, I noticed that the scorched part is, on all three, at the coil end. 

 

 

Expanding on this, what exactly exactly do you mean by the relay 'burning out'? You mean the relay stops working I imagine, and it goes black and crispy at the coil end? 

 

Have you measured the resistance across the coil pins of a burned out one to see if it is the coil going open circuit? It might not be. It might yet be one of the switches in it carrying too much current and failing. A bit of close inspection will reveal which pair of contacts, which it turn can be followed on your wiring diagram to a component which will probably turn out to be drawing more current than it is supposed to. 

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20 minutes ago, Mike the Boilerman said:

 

 

Expanding on this, what exactly exactly do you mean by the relay 'burning out'? You mean the relay stops working I imagine, and it goes black and crispy at the coil end? 

 

Have you measured the resistance across the coil pins of a burned out one to see if it is the coil going open circuit? It might not be. It might yet be one of the switches in it carrying too much current and failing. A bit of close inspection will reveal which pair of contacts, which it turn can be followed on your wiring diagram to a component which will probably turn out to be drawing more current than it is supposed to. 

Thanks again Mike.  Yes - you imagine correctly.

 

Picture below.   There are varying degrees of blackness within the box at the coil end only - and just a touch of scorching around the pins on a couple - also at the coil end.  All three relays I can now find are now open circuit between the actuating pins - and showing no resistance between common and not-actuated pins.  Also open circuit between the common and pulled-in pins.  So broken relays in the sense they won't now pull-in.

 

Thinking laterally - the switched live from the programmer directly supplies a wet-convector plinth heater i.e. fan and pipe sat only.  Nothing clever in the electrical sense.  The plinth heater should be, according to the spec, fused at 3A.  The output from the programmer is good for 10A resistive and 3A inductive.  The fan doesn't come in until the pipe stat reaches temperature - whereas the last two relays have burned out pronto.  But could the plinth heater be upsetting the switched live to the relay?  It is a few weeks since I took the plinth heater supply away the permanent live and connected it to the (programmer) switched live to reduce its tendency to run-on.  And faults are usually of my own making.

 

P1010061.JPG

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12 minutes ago, Tacet said:

Picture below.   There are varying degrees of blackness within the box at the coil end only - and just a touch of scorching around the pins on a couple - also at the coil end.  All three relays I can now find are now open circuit between the actuating pins - and showing no resistance between common and not-actuated pins.  Also open circuit between the common and pulled-in pins.  So broken relays in the sense they won't now pull-in.

 

Ok, so this points firmly at the coils heating up too much and the conductor breaking. 

 

Which is the original relay, i.e. the first one to fail? The one on the right I imagine. Light scorching like that is commonplace on boiler relays, even those still working. The other two look far more violent in their failure. I'll be most interested to hear what resistance the coil has on your next new one to arrive. 

 

 

12 minutes ago, Tacet said:

But could the plinth heater be upsetting the switched live to the relay?  It is a few weeks since I took the plinth heater supply away the permanent live and connected it to the (programmer) switched live to reduce its tendency to run-on.  And faults are usually of my own making.

 

Highly unlikely I'd say. Plinth heaters are very crude devices. The run-on is caused by the same pipe thermostat that holds it off until the pipe is warm. Even though the output air feels cool to the hand it will still be warmer than ambient while the pipes cool down. No harm that I can think of in re-wiring it as you have, but I know what you mean about self-introduced faults. Once the cause is established, the evidence was usually staring one in the face all along, if only one could see it!

 

 

 

Edited by Mike the Boilerman
Add a bit.

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1 hour ago, Mike the Boilerman said:

 

Ok, so this points firmly at the coils heating up too much and the conductor breaking. 

 

Which is the original relay, i.e. the first one to fail? The one on the right I imagine. Light scorching like that is commonplace on boiler relays, even those still working. The other two look far more violent in their failure. I'll be most interested to hear what resistance the coil has on your next new one to arrive. 

 

 

 

Highly unlikely I'd say. Plinth heaters are very crude devices. The run-on is caused by the same pipe thermostat that holds it off until the pipe is warm. Even though the output air feels cool to the hand it will still be warmer than ambient while the pipes cool down. No harm that I can think of in re-wiring it as you have, but I know what you mean about self-introduced faults. Once the cause is established, the evidence was usually staring one in the face all along, if only one could see it!

 

 

 

Very helpful Mike.  I had mislaid the first relay - but it's now turned up.  They have all been numbered.   But on the scorching scale, it is indeed about the same as right hand one shown (which was the first replacement and lasted maybe 36 hours).  Unlike all the replacements the first and original has a small amount of scorching at the contacts end.  But it only looks to be the usual amount from breaking for a few years.

 

I doubt the reason is relevant - but the running on of the plinth heater seemed to relate to the pipe remaining hot when the programmer was no longer calling.  I managed to persuade myself that it may have been thermosyphoning somehow - perhaps assisted by the fan.  I suppose it possibly depends on whether the pipe stat is on the flow and return etc.

 

In the meantime, I have connected  a pendant and domestic 10W LED to the troublesome(?) switched live to the boiler.  Admittedly, I made the connection at the house end to avoid standing in the garden.  The lamp lights up fine as and when expected - ,ie, when the cylinder stat or the room stat/programmer is calling - but not otherwise.  I don't have a clue whether an LED is more or less fussy than a relay when it comes to coulombs.

 

When the next relay arrives, I'll check the resistance across the coil. Then I'll put a non-boiler 240v across the coil and see what happens.

 

If it progresses to the next stage, I'll wire it to the switched contact side of the boiler - but energise the coils from a simple 240V with 5A light switch (MK of course) dangling through the window.  And see how it goes for a while.  The slight downside of this testing is that it probable won't switch in and out as often as it would if it was room and cylinder stat controlled.

 

Eventually, the penny will drop.

 

Edited by Tacet

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They are not 240v AC relay coils.

 

Unless someone has altered the mains in the property and you are getting 3 phase mains on the coil - massively unlikely -  there is no way they should burn up if they were 240v AC coils.

What do the markings on the relays say?

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10 hours ago, Boater Sam said:

They are not 240v AC relay coils.

 

Unless someone has altered the mains in the property and you are getting 3 phase mains on the coil - massively unlikely -  there is no way they should burn up if they were 240v AC coils.

What do the markings on the relays say?

 

If he had 3 phase in the house there would be 4 connection, not 2. 🤣

 

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11 hours ago, Boater Sam said:

They are not 240v AC relay coils.

 

Unless someone has altered the mains in the property and you are getting 3 phase mains on the coil - massively unlikely -  there is no way they should burn up if they were 240v AC coils.

What do the markings on the relays say?

 

That would be a good answer.  But all four relays are marked the same at 8A 250V.  The replacements were sourced from two suppliers (so, including the original, three sources).  Looking carefully at the printing on the cases there are three different styles which makes the dodgy batch/incorrect labelling less plausible.  It is just about possible that the original died of old age, the first replacement was faulty and the subsequent two replacements (which were from the same source) were from a incorrectly labelled batch.  But it seem less likely than the idiot-hypothesis which is usually proved correct in my case.

 

When the next relay arrives, I'll check the resistance across the coil.  Mike was suggesting 5k ohms to 50k ohms.  Putting aside changing resistivity and other stuff I don't understand, this gives a range of 12w to 1.2w.  My complete first guess was that it might take 1w to operated the solenoid.

 

32 minutes ago, cuthound said:

 

If he had 3 phase in the house there would be 4 connection, not 2. 🤣

 

 

23 minutes ago, Boater Sam said:

Not necessarily, just between 2 phases would give him 400v across the coil.

 

The statutory undertakers are not generous when it comes to mains services around here.   Mains water and a single phase, if you're lucky.  I have measured the voltage (with a simple multimeter) at the supply to the coil at 245V.  It could be something else when I am not watching - but it is enough to light a 60W LED. 

 

At one stage I did wonder whether the programmer might be supplying too low -  and causing more current to be drawn.  But that isn't how it works, is it?  The current drawn is a function of the resistance and the voltage -  there is no significant back EMF to interfere, is there?

 

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The relay has two different voltage specs: the safe voltage that can be switched by the contacts, and the voltage required to operate the coil. Just because it says 230v somewhere on the relay doesn't mean  the coil is suitable for 230v - that could be the contact spec. From the symptoms it does seem likely that the relays are burning out because you're putting 240v across a coil meant for 12/24/48v

 

Can you post a picture of the relay spec sheet or data plate?

 

MP.

 

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3 minutes ago, MoominPapa said:

The relay has two different voltage specs: the safe voltage that can be switched by the contacts, and the voltage required to operate the coil. Just because it says 230v somewhere on the relay doesn't mean  the coil is suitable for 230v - that could be the contact spec. From the symptoms it does seem likely that the relays are burning out because you're putting 240v across a coil meant for 12/24/48v

 

Can you post a picture of the relay spec sheet or data plate?

 

MP.

 

Exactly. The 8A 250v is the contact rating. The coil rating could well be 12v, 24v, 110v or whatever.

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1 hour ago, Boater Sam said:

Not necessarily, just between 2 phases would give him 400v across the coil.

 

True, but nothing else electrical would work for long either if that were the case.

 

 

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31 minutes ago, MoominPapa said:

The relay has two different voltage specs: the safe voltage that can be switched by the contacts, and the voltage required to operate the coil. Just because it says 230v somewhere on the relay doesn't mean  the coil is suitable for 230v - that could be the contact spec. From the symptoms it does seem likely that the relays are burning out because you're putting 240v across a coil meant for 12/24/48v

 

Can you post a picture of the relay spec sheet or data plate?

 

MP.

 

 

 

Not in my limited experience. The contact rating marked on a tiny relay like this is usually expressed only in current, and the coil rating is usually expressed only in voltage. So 8A 250V means 8A switch rating, 250v coil. 

 

 

34 minutes ago, Tacet said:

When the next relay arrives, I'll check the resistance across the coil.  Mike was suggesting 5k ohms to 50k ohms.  Putting aside changing resistivity and other stuff I don't understand, this gives a range of 12w to 1.2w.  My complete first guess was that it might take 1w to operated the solenoid.

 

The (more substantial) coils on 240v gas valves in boilers are typically between 2 kOhm and 4 kOhm. That is why I suggested 5kOhm or much higher for this relay.  They are just very approximate values, estimated to help you differentiate between a coil for 240v and a coil for 12v.

Edited by Mike the Boilerman
Add a bit.

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THe contact rating should specify the voltage and whether it is DC or AC, it makes a big difference. DC is much harder on switch contacts due to arc on break.

I still say that the coils are not 240v AC coils, 3 burning up is more than bad luck or coincidence. The coil spec should be on there somewhere, as a voltage and as AC.

 

I would expect 2 to 3 watts to energise. Checking the resistance of the coil will prove the working voltage, there will be a huge difference between a 12v and a 240v coil.

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35 minutes ago, MoominPapa said:

The relay has two different voltage specs: the safe voltage that can be switched by the contacts, and the voltage required to operate the coil. Just because it says 230v somewhere on the relay doesn't mean  the coil is suitable for 230v - that could be the contact spec. From the symptoms it does seem likely that the relays are burning out because you're putting 240v across a coil meant for 12/24/48v

 

Can you post a picture of the relay spec sheet or data plate?

 

MP.

 

 

29 minutes ago, nicknorman said:

Exactly. The 8A 250v is the contact rating. The coil rating could well be 12v, 24v, 110v or whatever.

 

7 minutes ago, Mike the Boilerman said:

 

 

Not in my limited experience. The contact rating marked on a tiny relay like this is usually expressed only in current, and the coil rating is usually expressed only in voltage. So 8A 250V means 8A switch rating, 250v coil. 

 

 

 

Thank you everyone.

 

Datasheet attached - but it doesn't help much as it covers a range of relays with various coil voltages.  But here is a link to the item purchased from this supplier:

 

https://uk.rs-online.com/web/p/non-latching-relays/0376824/

 

The datasheet does show a blue relay (as the 240V coil version) and the link as yellow.  I have (four and counting) yellow ones.

 

The postman has now been - but not delivered the daily relay.  When one does arrive, I'll measure the resistance across the coil which should(?) help identify its intended voltage

 

 

 

 

 

 

 

 

0900766b8138b9fb.pdf

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9 minutes ago, Boater Sam said:

THe contact rating should specify the voltage and whether it is DC or AC, it makes a big difference. DC is much harder on switch contacts due to arc on break.

I still say that the coils are not 240v AC coils, 3 burning up is more than bad luck or coincidence. The coil spec should be on there somewhere, as a voltage and as AC.

 

I would expect 2 to 3 watts to energise. Checking the resistance of the coil will prove the working voltage, there will be a huge difference between a 12v and a 240v coil.

Thank you.  There some minor differences in the printing of the various logos - but all are identical with the --/-- 8A 250V ~  

 

P1010062.JPG.3e32ba26c334a98d4efa95a2a5986537.JPG

 

 

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Just a thought - have you tested the mains voltage? I have a feeling that a fault on the "earth" line away from your property might put the full 3 phase voltage onto your circuits or with a resistance on the line possibly only part of it. I also suspect that if it is resistance somewhere down the companey's "earth line"  the actual  voltage at home may vary according to other users demand on the system

 

Could all be ollucks so wait for comments from proper mains type people.

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Reading that relay case,    contact, 8 Amps @ 250v AC.  Exactly as I said, its the contact rating only.

So it is NOT a mains coil!!!!

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It's not unknown for the parts houses to supply the wrong thing. I've just gone to my stash of parts for my lithium battery project and opened a bag from a Farnell order. The label on the outside of the bag has the manufacturers part no.  I ordered. The chips inside the tube are something completely different.

 

MP.

 

ETA: The 8A 250V rating in the picture definitely refers to the contacts. There doesn't seem to be a spec for coil voltage there.

 

EATA: Datasheet here: https://www.finder-relais.net/en/finder-relays-series-40.pdf

Page four explains how the long-form part number relates to things like coil voltage and contact material. Can you find a part number that looks like

40.52.8.230.0000 anywhere?

 

Edited by MoominPapa

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4 hours ago, Tacet said:

 

 

 

Thank you everyone.

 

Datasheet attached - but it doesn't help much as it covers a range of relays with various coil voltages.  But here is a link to the item purchased from this supplier:

 

https://uk.rs-online.com/web/p/non-latching-relays/0376824/

 

The datasheet does show a blue relay (as the 240V coil version) and the link as yellow.  I have (four and counting) yellow ones.

 

The postman has now been - but not delivered the daily relay.  When one does arrive, I'll measure the resistance across the coil which should(?) help identify its intended voltage

 

 

 

 

 

 

 

 

0900766b8138b9fb.pdf

 

Clicking on  RS link in the post above, and then "Technical Specifications" provides this information, which clearly indicates coil voltsage to be 230V and contact switching voltage to be up to 400V ac.

 

Technical specifications

Coil Voltage 230V
Contact Configuration DPDT
Switching Current 8 A
Mounting Type PCB Mount
Terminal Type Through Hole
Series 40 Series
Coil Resistance 28 kΩ
Maximum Switching Voltage (AC) 400V ac
Application PCB
Length 29mm
Depth 12.4mm
Height 25mm
Dimensions 29 x 12.4 x 25mm
Operating Temperature Range -40 → +85°C
Minimum Operating Temperature -40°C
Maximum Switching Power (AC) 2 kVA
Maximum Operating Temperature +85°C
Isolation Coil To Contact 6kV
Contact Material Silver Alloy
Coil Power 1.2W
CAD Drawing 3D CAD Model

 

Perhaps RS have wrongly packed  24 Volt coil relays in 240 volt relay packaging? Easily proved, as MtB says by measuring coil resistance.

Edited by cuthound
To add the last sentance

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4 hours ago, Tony Brooks said:

Just a thought - have you tested the mains voltage? I have a feeling that a fault on the "earth" line away from your property might put the full 3 phase voltage onto your circuits or with a resistance on the line possibly only part of it. I also suspect that if it is resistance somewhere down the companey's "earth line"  the actual  voltage at home may vary according to other users demand on the system

 

Could all be ollucks so wait for comments from proper mains type people.

Thanks you

 

Yes - with a simple multimeter at 245V

4 hours ago, dor said:

Yes - but this is the one that I believe has been ordered and re-ordered

https://uk.rs-online.com/web/p/non-latching-relays/0376824/

 

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I suspect that may be tad high but wait to see what others say. Worth checking again when everyone gets home and starts cooking. I would expect it to be lower but if its higher then there may be a company cable problem but again my knowledge is very sketchy in this area.

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