Ideal RD2 450 - Thermistor

[Schmill]

Does anyone know off hand what resistance I should 'expect' on the thermistors on this boiler?
I knew it once before (when I had to replace them), but have since forgotten
I know that OC or SC would be obviously faulty, but I'd like to know roughly what range I should expect to see (cold boiler).

As some background the boiler nicely comes with a diagnostic flow chart, but I think it is pretty much redundant, as I have LED3 flashing >1 per second, and the table at the bottom of the chart indicates that as "Sensor Fault".

RD2 Fault Finding Page

• Schmill
• 25 Apr 2012
• 1

Also, does anyone know if 'Sensor Faults' is limited to just meaning the thermistors, or would the APS also be covered by this?

Thanks!

 

[mickyg]

if thats the one with the red, white and blue wire sensors all on the same harness then that will be your fault, they are total junk. Its always the red one but you cant change them individually. There's an interesting story behind why it has those rubbish things as well

 

[Schmill]

if thats the one with the red, white and blue wire sensors all on the same harness then that will be your fault, they are total junk. Its always the red one but you cant change them individually.

Yup, thats the one;

Flow, return, and flue (I believe)
Been checking other things on the boiler as I wasn't sure it was going to be the sensors again, as I only changed the set a few years back!
Of course in an ideal (no pun intended) world I'd remember where I had put the old harness on the off chance that it was a different sensor last time..... but I can't

Seems to be a wide range of prices for replacements too!

There's an interesting story behind why it has those rubbish things as well

Anyhoo... what's the story?

 

[Schmill]

Quick update of the readings on a cold (brrrrrr!) boiler, (sensors disconnected from the control PCB):

Grey (Flue): 142 kOhms
Blue (Return): 14.5 kOhms
Red (Flow): Open Circuit

So I know the Red / Flow thermistor is faulty, (as predicted), but but does anyone know what value it is 'supposed' to have, and also whether it is possible to substitute either the grey (or more likely) the blue from the old harness (if I can find it) in order to get the boiler up and running until I can get the replacement harness?

NOTE I don't want to do anything unsafe, but if the 'blue' and the 'red' thermistors are known to be the same then this would seem like a reasonable approach, otherwise we'll just all huddle together under some blankets until I can get a replacement delivered

 

[Schmill]

Ok... a truely bizarre development...

In order to test the resistance of the thermistor I had popped the contacts for it out of the connector block.
Checked it several times - open circuit.
Flexed the wires in case of damage - open circuit.
Decided to pack it all away and order a new thermistor harness, push the contacts back into the connector, and decided to probe them one more time... 14.5 kOhms....

Twisted the wires, flexed the wires, wiggled the connectors on the wire, wiggled the wires at the point that they enter the thermistor.... 14.5 kOhms!

Reconnected the thermistor harness to the control PCB and powered up the boiler... all started fine. Monitoring the voltage on the flow thermistor I could see it gradually drop as the flow temperature increased.

To all intents and purposes it seems to be working again.

It makes me wonder what was wrong with the thermistor harness is the first place, and now I'm wondering whether I should order a replacement harness anyway, although they are quite pricey for 'just-in-case'.

Tempted to wait for a day or so and see if it 'behaves' or whether it goes faulty again...

 

[mickyg]

another thing you can do is crimp the red sensor with some pliers until you hear a crack noise, that usually gets it going again ! temporary of course


As for the story, well Ideal obviously had a perfectly good boiler in the original FF Classic boiler, and this revised version is no more efficient, so why the changes?
Well, are friends at British Gas thought wouldnt it be a good idea if they could remotely tell if a boiler breaks down? They're "vision" was to be knocking on your door to tell your boiler had broke before you knew. So they went off to their good friends at Ideal, and asked them to make a boiler which had sensors and a smart pcb so you could plug a phone line in and a signal would be sent up the phone line to tell an office what the fault was.
So Ideal make the boiler(have a look at your pcb, maybe a phone socket on there) British Gas started fitted them but ditched the idea
So you have a boiler with capabilities of which it will never be used ! and its less reliable than the equally performing ideal classic that came before

 

[Whitespirit66]

Thanks for the story Micky. Been waiting for that.


What with all the News Of The World goings on, not sure if I would want BG hacking into my boiler.

At least they never stop trying to look after our world.

 

[Agile]

I think that some of the PCBs did not have the phone interface installed probably when it was realised they were not to be used.

There were some other models with the phone interface designed in too.

Tony

 

[Schmill]

Thanks for the story Micky, an interesting read to be sure.

Well this morning I woke up to a warm house
However when we used the hot water the boiler started, and stopped, started, lit, and stopped... started and stopped, started, lit and stayed lit.
So it's still having problems... does this sound typical of faulty thermistor behaviour?

To confirm, mine is one of the ones with the modem board fitted. Often wondered why, especially as it isn't connected to anything outside of the boiler!

Any recommendations on where to buy the harness from? Feel free to PM if posting on the actual forum reply would fall foul of the 'advertising' rules.

 

[Schmill]

Nobody has any recommendations on where to buy the harness?
I've searched around the 'net' but there seems to be a suspiciously high number of websites with differing names, but the same layout, look, and price. Would prefer to go to a trusted seller if one could be recommended?

Thanks!

 

[nickso]

make sure you get the right version at least. They are different for wall mounted and floor mounted boilers, possibly wire length only though.

 

[Schmill]

Yup, no worries about that, got the part number

Now ordered

 

[plummerman]

Not to throw a spanner in the works but i regularly go on jv's with BG lads to these

BG lads 'we've fitted several harness, several boards' and yet the damn led3 lockout keeps coming back

Right have you checked the resistance of the plate ignitor? Anything more than 90 ohms boiler logic thinks its not lit and led will come on

So matey id just have a check of this before you fire a harness in.. Glow plug is a lot cheaper than a harness

 

[petit_pablo]

Not to throw a spanner in the works but i regularly go on jv's with BG lads to these

BG lads 'we've fitted several harness, several boards' and yet the damn led3 lockout keeps coming back

Right have you checked the resistance of the plate ignitor? Anything more than 90 ohms boiler logic thinks its not lit and led will come on

So matey id just have a check of this before you fire a harness in.. Glow plug is a lot cheaper than a harness

I never knew that! Thanks will have to remember that one.

 

[Agile]

Its not an approved repair, but in an emergency until the correct part can be sourced an old return NTC can be used to replace the flow NTC.

I have a brand new set which I bought when a customer thought his had failed. It turned out the gas meter had been stolen!

Tony