Junior 28i problem

[smiffy6969]

Hi,

I had an issue with this boiler 2 years back, basically the igniter was firing 3 times stopping and then doing nothing, due to this the boiler wouldn't fire up.

I was told it would be the low pressure sensor, the one that sits near the top right hand corner of the boiler. I drained the system, took the valve off, cleaned it out, put it back on, flushed the system and got it working again.

This solved the issue we had and it was fine after that.

A week ago I had a very similar issue, the warning light was flashing, so I reset the fault, and the water was working fine.

I switched the heating on a few days ago and after about 10 min of it being on, the heating stopped, warning light was flashing. I waited, reset the boiler, and as soon as the heating came on it went straight to warning again flashing the red light.

I played with it for a few days, and found that the hot water runs fine, you can fill whole baths without an issue. The minute the heating goes on, the 10 min later the red light is flashing.

I changed the low pressure sensor today, thinking this was still the problem, got the system fired up again and it seemed ok for about half an hour, then the wife switched the hot tap on, washed her hands and switched off, i thought oh no, the boiler did not refire for the heating immediately but did after a few minutes, few......

Left for another 10 min and i washed my hands, oh, guess what the warning light comes on after i turn the tap off.

So any ideas........... it's not the low pressure switch cause thats been changed, we have really bad hard water round here, it's terrible, I am thinking it seems to have trouble switching between the hot water and the heating, I am going to do a full power off for an hour, fire it up, ban anyone to see if the heating can stay on long enough, if it is fine, then is there a switch or valve that selects water or heating, cause I am beginning to think maybe something else is caked up with gunk and limescale.

If I am off the mark here, please point me in the right direction.

thanks in advance

Paul

 

[OLLIE20]

Is it the standard efficiency junior, is it the red oval light thats flashing, how many times a second is it flashing????

 

[smiffy6969]

Hi,

it's flashing real quick, like 5 times a second at least.

I just tried running the heating only, without touching the taps. Here is what I have found.

If you run the taps, it works fine, you can fill whole baths and it works without an issue.

If you put the heating on, the heating heats up, once at temp the boiler goes out, after about 5 min or so when it's cooled down a little, and it's time to fire the oiler up the second time to keep the heating up to temp, this is when it fails with fast flashing big oval light.

If the system is cold, it will fully heat up and turn off, then when cooled and time to relight, it fails.

If system is hot, it will heat up to temp, then turn off as normal, but when it tries to turn on the second time it fails.

So in summary, hot water is perfectly fine (until heating messes up, then no hot water), heating works fine the first time it is fired up, but then once at temperature, and it turns off the flame, it does not come back on.

Also if you work the taps while the heating initially heating up, it seems to switch from heating to taps and back to heating ok, so the only thing I can think is the issue is when it is up to temperature, it fails to re-fire and throws the red warning light.

The boiler model I do not know, but just uploading image.

thanks

Paul

 

[OLLIE20]

4 times a second could mean a number of things, your CH sensor might be going open circut when it get to temperature and locking out boiler, it can also happen due to faulty harness PCB (common on these) and a few fan ans APS faults, condensation in tubes, or fan sticking etc, but all need a RGI to check, sorry, its gonna cost you

 

[smiffy6969]

sorry took so long, bloody phone messy me about now.........

Untitled

• smiffy6969
• 29 Sep 2010
• 1

 

[smiffy6969]

when you say ch sensor going open, we talking the temp sensor behind the low pressure valve, this is a standard temp sensor like what you get in washing machines (im a electronics engineer). This thing tripping out when at temp (it's inline with the low pressure sensor in series with it), cause it's giving a similar error to last time it wnet wrong and it's inline with low pressure sensor that went wrong last time.

 

[smiffy6969]

i can test this by isolating this sensor and running system with it isolated, I did this with the low pressure valve to test it was that when it went wrong two years ago, then when I was happy it was that, took off and cleaned it.

Paul

 

[OLLIE20]

Oh ok can go into a bit of detail then, the one behinf the LWP switch is an o/ht stat, which is just a simple open and close switch, will be closed upto a certain temp and will open above set temp and break circut shutting down boiler

The CH sensor or Thermister as it is referred to is a NTC sensor, as the temp in your CH rises the Resistance through it drops, relaying signal to your PCB and back to gas valve controling the gas pressures etc, what can sometimes happen is when it heats they can go open circut and cut out boiler, but once you check it when its cooled all will seem normal

 

[OLLIE20]

Mate you know you shouldnt be going in the combustion chamber, realy you have to do a load of gas safety checks on boiler once you've been in there P.S. thermister isnt in there anyway

 

[smiffy6969]

Ok, thanks alot,

I will try bypassing the thermal cutout behind the LP sensor, as this is simple, I will run the system for as long as i can but no longer than an hour to check if it still cuts out, keeping an eye on the temperatures in the radiator etc.

I have not been in the chamber at all, I would never mess with gas, I have only looked at what is external to the chamber, the chamber is behind the second metal panel isn't it.

Where is the NTC sensor is it in the chamber, if so, I will have to get someone out if it is not the thermal cutout.

Paul

 

[OLLIE20]

No mate the 2nd one is the burner box, the outer one is the combustion chamber, which you have already removed if you can see LWP switch and O/ht cut out

The thermister is behind PCB drop down and hook onto bottom hooks, so it doesnt dangle and there is a red sensor with to red wires going to it that clips to a pipe, that you ch thermister

I musr advise you not to do this work yourself mate, although DIY gas work is a grey area, i dont recomend it and on your head be it, but its down to you at the end of the day

 

[smiffy6969]

ok, I totally understand, thanks for the advice, maybe it is time to call someone out.....