Condensing problems?

[tridimnaw]

What causes condensing oil boilers to stop condensing?
Ive been to a couple of boilers recently where the traps have dried up!!
I dont have this problem with worcester bosch, mainly warmflow and grants, what causes this?
My boss doesnt seem to answer me when i ask him about this, just says its one of those things, and tells me to fill up the trap with water.
Ive been servicing and repairing boilers for about 6 years now and have not come across this untill now!!

 

[Dotty]

Undersized boiler with the return not hitting 55°

 

[tridimnaw]

Is that still applicable to combi boilers? I know the fgt in warmflows if higher than other boilers, does that play a part in it? I had to replace a door seal on a warmflow today as the rubber was heated and gone brittle and dissintigrated!! I like to understand why things happen so this bugged me a fair bit!!

 

[Millsy 82]

I followed someone who used to drop the co2 down but the flue temp would go up and it use to kill the baffles so that could probably do something like that.

Also system not set up correctly.

 

[Best]

Is that still applicable to combi boilers? I know the fgt in warmflows if higher than other boilers, does that play a part in it? I had to replace a door seal on a warmflow today as the rubber was heated and gone brittle and dissintigrated!! I like to understand why things happen so this bugged me a fair bit!!

Both answers given are reasons why boiler won't condense.
I would think a very strong possibility is too much air adjustment for the burner.
Simple way to test is when you are setting a condensing oil boiler with low flue is just turn air up about 10 or 20% and you will see plume stopping. Obviously not right to have boiler going like that and very inefficient.
The door seals on the Warmflows secondary heating exchanger will disintegrate in 2 or more years. This is partly due to higher fgt of those boilers and the fact it is just a rubber seal.
Warmflow recommend you change those 2 years max. It is a flue seal basically and fumes will escape, so I replace them every year. Grant boilers better design and lower fgt

 

[tridimnaw]

Cheers for all the input guys

 

[oilman]

It can be a balancing issue. The returning temperature should be BELOW 55 degrees.
(pre condensing was often set at 11 degrees for radiators)
the system differential should be 20 degrees for radiators or 10 degrees for underfloor heating
A differential of 20 degrees is correct across each radiator size the radiators based on a 60 degree operation. so if the flow is 70C with rads the return should be 50C with Underfloor the flow is lower ie 50C and returns at 40C. when filling in the CD11 commissioning form the flow and return pipe temperatures should be measured and recorded. GOING back to the old system with 11C differential and the new boiler flow of 70C the return will be 59C and there will be NO condensing.