Potterton Kingfisher - overheating really badly - help

[BrianU]

Potterton Kingfisher floor standing boiler - about 8 years old
Gravity HW pumped CH
All rads have Thermostatic Valves
Do not have a central room thermostat
System working happily for the four years that we have been in the house.
All rads bar one, and all rad thermostats replaced four years ago

Aggravating factor - 3 year old child and 10 month old baby to consider.

The Story so far -

Started to overheat Xmas 2006 - CH Header tank was boiling and overflowing via overflow vent in to CW tank, loft space full of steam condensing all over stored items - nasty
Called Corgi registered local heating engineer - won't come out till new year.
New Year - Engineer arrives - says its the thermostat - needs replacing - will order and replace. Says that overflow from header into CW tank is a no-no and should be replaced to overflow independantly outside - sensible. Also, CH system is clogged and needs Powerflushing - agreed this would be a good idea - can't do the powerflush and overflow until early Feb (bit of a wait really, but okay)
One week later
Engineer replaces themostat, checks it's working - paid
That evening - boiler stops working and goes into lockout mode - I tun off, re-set, starts up again. Rads are full of air.
Next day - call engineer - arrives same day (good) bleeds rads -
Shortly afterwards - CH systems isn't functioning properly
Call engineer - who advises that this may be so until the system is powerflushed
Wait and hope.........
Boiler overheats again - dirty CW tank, loft full of steam etc
repeat occasionally until
Feb 2007 - Engineer power flushes system and replaces overflow - boiier thermostat now has to be turned right down low now (dot 2 or 3 on scale) - paid
Afterwards
Overheats again - this time the new plastic replacement pipe from the CH header tank collapses from the heat, almost melted !!
Call engineer - can't come out for a week (I'm really ticked off at this point, but refrain from getting irate as consider that this will not help (danger to children explained) )
Can't seem to bleed upstairs rads - used to be able to do this easily - bit odd!
Rads behaving oddly -as in themostats seem to be able to get stuck open - wierd!
Overheats again - scalding water - loads of steam in loft etc etc
Waiting for engineer - due 14/02/2007

start to look for other sources of help in advance of him arriving - need some ammo!

I can't pin down when the problem happens to a specific set of circumstances - sorry


Can someone please give me some advice about this problem, I'm really frustrated, as it's been dragging on far too long.
I have read some posts on the site which seem to relate to similar problems - but I'd really appreciate a response specific to this problem in order that I don't get charged for a load of components that may not need replacing. We've already spent over £500 and can't afford bills for unnecessary replacement of components if they are not required.
Any and all advice will be gratefuly received.

P.S. I'd like to apologise in advance if I've done anything inappropriate in this post - I'm a newbie in this respect - so please be gentle with me!

 

[Agile]

I cannot see that you have done anything wrong.

I have some difficulty in knowing which model you have when you say it has gone to lockout! At that age I doubt it would be the KF MF but that is the only KF which I think can go to a lockout but I dont think its allowed to be on a gravity system.

I will assume that its an early simple KF. These have a thermostat which turns off the gas valve when it gets hot.

If the boiler is overheating then there are only two causes. First a stuck on stat but this has been replaced and should be OK if properly fitted.

The only other posibility, although this is very rare, is that the gas valve is sticking on!

You can check for this if you have the time by regularly turning the stat down until it clicks off and checking that the flame goes out every time. You might have to wait a lot of time as this can be very intermittent like once every two weeks!

As for the rads, that may be a consequence of the power flushing. Since I dont know how he did it or what chemicals he used then i cannot comment on this.

Tony Glazier

 

[BrianU]

Hello Tony

Thanks for replying

I have checked, and the boiler is the MF CF 60, and is actually 9 years old this month - I found the receipt.
I don't know what chemicals were used in the flush as I wasn't present when it was done, so unfortunately I can't throw any further light on that one.
I have looked in the installation manual for the boiler, and there is an option for an "open vented gravity domestic hot water and pumped central heating system" so that seems okay.
I have had to turn the stat down further again this evening as the water in the system was starting to boil again. Water in the HW tank is too hot to stand.
If its any help, there tends to be a lot of relay clicking action when the boiler reaches temperature, like its confused about what to do. I'm pretty sure that it used to just click once and stop heating. Is it likely to be a problem with the controller PCB?

Brian

 

[Agile]

OK it must be one of the first Potty KF MFs.

I am slightly surprised that it permits a gravity HW circuit but OK.

On the face of it then it does sound as if the PCB may be faulty however before changing it I would check the hot and cold resistance of the NTC sensor AND that its properly bedded in some NEW thermal transfer paste! You can heat it with a hair dryer but dont OVERheat it.

Has the NTC sensor ever been removed before?

The good news is that the PCBs are not all that expensive as compared with the Suprima for example.

Tony

 

[baxpoti]

Thermistor
Potentiometer
PCB
In that order financially

Can't remember the last time I changed a potentiometer and the sensor been changed?

 

[BrianU]

Hello Tony

Is the NTC sensor the Thermistor? if so, this was replaced by the engineer on the first visit. I looked at the old thermistor and tried to check it out (no conclusion - not really sure what to look for on the multimeter) it did have some thermal paste around it, I would assume that the engineer applied paste to the replacement if this is the correct thing to do - perhaps I should check!.
I'm relieved to hear that replacement PCBs are not too expensive.

Appreciate your help Tony


Brian

OK it must be one of the first Potty KF MFs.

I am slightly surprised that it permits a gravity HW circuit but OK.

On the face of it then it does sound as if the PCB may be faulty however before changing it I would check the hot and cold resistance of the NTC sensor AND that its properly bedded in some NEW thermal transfer paste! You can heat it with a hair dryer but dont OVERheat it.

Has the NTC sensor ever been removed before?

The good news is that the PCBs are not all that expensive as compared with the Suprima for example.

Tony

 

[BrianU]

Hello Baxpoti

Thanks for your advice.

Yes, the thermistor has been changed, I'll certainly suggest to the engineer that the the pot is a possible candidate for replacement, before he fits a new PCB, although from your post, it would seem that the PCB is now most likely to be at fault!

Brian

Thermistor
Potentiometer
PCB
In that order financially

Can't remember the last time I changed a potentiometer and the sensor been changed?

 

[Agile]

Hello Tony

I would assume that the engineer applied paste to the replacement if this is the correct thing to do - perhaps I should check!.

Brian

You might assume that but I would never assume anything.

I know that only a very few engineers ever carry or even understand what the paste is for.

After 9 years the original paste will be well dried up and will not be in intimate contact with any refitted sensor either new or the original.

I recently advised a very sceptical engineer about this on a KF and he later reported that it had solved the overheating problem !

Tony

 

[BrianU]

Hello Tony

This is really interesting. The old thermistor had some white paste left on it, but from what you have said, it may well have been too little to be effective, and so it also follows that the old thermistor might still have been working if some more paste been applied.
I'm going to take a look at the new thermistor tonight when I get home and see if the engineer has put any paste on - I have a suspicion that this is not so! - it could easily explain the continuing problem.
You may well have saved me a lot of time and money.
I'll let you know the result tonight when I have checked.



Thanks again for your help


Brian

Hello Tony

I would assume that the engineer applied paste to the replacement if this is the correct thing to do - perhaps I should check!.

Brian

You might assume that but I would never assume anything.

I know that only a very few engineers ever carry or even understand what the paste is for.

After 9 years the original paste will be well dried up and will not be in intimate contact with any refitted sensor either new or the original.

I recently advised a very sceptical engineer about this on a KF and he later reported that it had solved the overheating problem !

Tony

 

[BrianU]

Hello Tony,

I have just removed the front cover of the boiler and removed the thermistor to check, and ....... guess what..... not even the faintest smear of thermal paste on the new thermistor!
The engineer is already booked in for tomorrow, so I'll leave a note suggesting that this should be the very first thing that is done to try and solve the problem.
I'm really not very happy that a Corgi registered engineer would not know the importance of this simple task. Even if it does not solve the problem tomorrow, it should still have been done as a matter of course.
I can feel the beginning of a rant coming on, so I'll stop here and report back to you tomorrow after he has "fixed" it (or not, as the case may be)

Thanks again

Brian

Hello Tony

I would assume that the engineer applied paste to the replacement if this is the correct thing to do - perhaps I should check!.

Brian

You might assume that but I would never assume anything.

I know that only a very few engineers ever carry or even understand what the paste is for.

After 9 years the original paste will be well dried up and will not be in intimate contact with any refitted sensor either new or the original.

I recently advised a very sceptical engineer about this on a KF and he later reported that it had solved the overheating problem !

Tony

 

[ACOperson]

Fairly certain its the paste from what you've said.

Make sure that the overheat stat is stood off of the pipe as per Pott instructions due to your gravity hot water circuit.

 

[Agile]

Ha! Ha! Sceptical !

 

[baxpoti]

ooh, the quality of engineers out there.

The old saying rings true, again....

'Never assume always check'

 

[BrianU]

Hello Tony

We've got rid of the engineer, who turned up, told us that the thermistor (which he had already replaced) was faulty, and that we would have to wait till next week before he could come back and fit another (we've been suffering from this problem for six weeks already since we first called him out) - what a complete tosser. He wasn't even prepared to try the thermal paste solution.
At this point I'm banging my head against the wall.
Fortunately, my clever wife managed to locate, via a friend, another very helpful engineer who turned out this afternoon to help. He was prepared to try the thermal paste solution, and even checked with Potterton themselves - who suggested the same - spot on Tony!
Unfortunately, it hasn't worked - and I'm really disappointed.
Still, at least we've found someone who will make an effort with some degree of urgency!

Oh well, next stop Potentiometer or PCB - probably PCB judging by the unusual clicking noises.

Thanks to everyone who contributed suggestions, we really are very grateful for your input.


Brian

 

[Agile]

"""Still, at least we've found someone who will make an effort with some degree of urgency!

Oh well, next stop Potentiometer or PCB - probably PCB judging by the unusual clicking noises."""

It takes about 15 seconds to check the potentiometer! Why did he not do that during his visit?

I am sorry that the paste has not solved the problem in this case. You must understand that the sensor needs the thermal paste and sensors should never be removed without adding it on replacement.

Now the sensor is correct you can move on to the next part, the potentiometer, however thats such a simple test I dont understand why this helpful engineer has not done it!

I never have to keep calling Potty so whilst he may be helpful I still doubt his technical competence! All I can say is that he may be more helpful than the last.

Tony