Problem with a Halstead Finest Combi boiler

[cjhiggins]

Hi all,

i'm having trouble with the boiler mentioned in subject. I think it may be a pre 2001 ace.

Problem is when HW is run the boiler starts up fine, runs for about 20 seconds and then the burner will go off, wait for 10 seconds or so and then the burner will come back on and repeats like this.

I read on a another forum that sometimes the heat exchanger can get clogged if its not installed properly so i drained the system and removed it, flushed it out and a fair amount of black crud did come out. replaced the heat exchanger but still had the problem.

I checked that flow switches were working and cleaned them for good measure...still had the problem.

Next I thought it maybe one of the thermistors giving a bad reading, so i thought rather than spending £30 each on 2 thermistors i would buy a couple of 6kohm resistors, to frig the system and identify that the problem was the resistors. (thermistors read 10k at 25 degree, Negative curve)

I thought I had cracked it, with a resistor in the end of the lead for the CH thermistor and plugged in as normal on the HW the boiler seemed to work fine, after a minute or so tripped on overheat, which i was expecting due to giving it a false reading.

So i popped out and bought a thermistor, swapped it over and i still have the problem...

I am now wondering if the burner is not modulating. Is there something in the program that says to turn off the burner at a certain temperature before its reached the temperature for a safety lockout?

I measured the DC voltage going to the modulating gas valve and when the burner starts it rises rapidly to 18v and stays there until the burner goes off. is that normal?

Another thing, I thought i would try swapping the thermistor leads around, so the HW was on the CH tthermistorand so on,

Strangely the burner did not go off, but the hot water was being diverted to the CH and not the HW I cant get my head around that to be honest.

Any help would be greatly appreciated.

Chris

 

[adlplumbing]

their are few things i can think of but you need get rgi out to look at them

 

[ChrisR]

Your plate hex is still blocked
and your diverter isn't working properly.
Entirely normal!

 

[cjhiggins]

I cant see a way to remove that plate hexchanger....
I have just been looking through the installation manual and it only describes the main hexchanger. any tips?
Cheers
Chris

 

[picasso]

As you look at the phe from above you will see 2 allen bolts , its these 2 bolts that hold it in place, obviously if you havent drained the boiler and shut off the cold supply your going to get rather wet.

 

[cjhiggins]

Cheers

 

[cjhiggins]

thanks everyone so much.
took the plate heatex off, and a load of crap came out, flushed it through. stuck it back on and hey presto. hot water

Thanks again, got our first baby on the way so fixing this has been a life saver.

Chris

 

[Agile]

It seems that the first heat exchanger that you removed was in fact the MAIN primary heat exchanger!

That should only be removed by a registered gas engineer!

Anyone can remove and clean the plate heat exchanger.

But shaking them out only removes some of the dirt. It needs chemicals to do the job properly.

Tony

 

[cjhiggins]

it was the main heat exchanger i removed first. was no need to touch any of the gas fittings/supply so felt confident to remove it, only 2 nuts.

I flushed it through with some electraclean. probably not the best stuff but will have to do until I can get something better.
Cheers

 

[ChrisR]

Electraclean wouldn't do much!
Try kettle descaler crystals, or hydrochloric acid - if you know how to handle it.

Put the hot water (tap) on. If the heating pipe starts to get hot then the diverter isn't working 100%.

Removing the main heat exchanger involves the combustion chamber which means you could have left something wrong which could be dangerous - According to Corgi/GSR.
How big a danger that is varies with the boiler, hence the advice.