WB CDi37 Classic permanently on minimum output

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The boiler is about 12 years old and was working correctly until a few days ago when it decided to go on strike - no heating or hot water. The pressure had gone down to zero. I tried to repressurize it but had diffuculty fitting the key - so did my son, who pointed out that there was some water on the undertray. I phone my engineer who visited late that afternoon.

He repressurized the boiler and said that the water on the unndertray had dripped from the condensate pipe connection. As the boiler was workng he said he would come back yesterday (which ended up as this morning) to fix the condensate pipe.

This morning, the boiler was off and displaying the F7 error code. I informed the enginer when he arrived and that the boiler was turning on and off continually. He said it sugested the condensate pipe was frozen. (It's a 21mm plastic pipe which comes down the side of the house from the airing cupboard on the first floor. A quick check prooved the pipe was blocked so he set about unblocking it with kettles of boiling water. Another check and he declared it unblocked. He then replaced the faulty connection between syphon and discharge pipe. When he left, the boiler seemed to be working correctly, eventhough the house was cold.

However, we soon noticed that the house was taking a long time to heat up. A quick check showed that the boiler was only getting up to 55C, stopping, dropping to 45C, then restarting. It normally gets up to 75C without any problems. So I checked all the boiler parameters - they were all correct. I then checked parameter 9.c (actual heat output). When the boiler ignited it went immediately to 50%, but then dropped quickly to 32%, the minimum, and stayed there.

I then checked parameter 4.F (syphon fill program) which showed 1 - on, min output. I changed this to 0 and saved the changes. The boiler restarted and the water is now getting hotter.

Why would the boiler stay on minimum output after the syphon has finished filling?

I have reset parameter 4.F to 1 as the manual says it should only be turned off to carry out servicing work.
 
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Why would the boiler stay on minimum output after the syphon has finished filling?

I feel like I'm asking the obvious here so forgive me if it sounds patronising, but might it not have realised the syphon had finished filling? More to the point perhaps, I assume it had actually finished?
 
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I feel like I'm asking the obvious here so forgive me if it sounds patronising, but might it not have realised the syphon had finished filling? More to the point perhaps, I assume it had?
Good point. The display only shows the flow temperature. When the syphon is filling it should be showing -//- alternating with the temperature, which isn't happening. This suggests a fault in the PCB. Maybe resetting all parameters would help?
 
Reset all parameters this morning (8.E = 0). The boiler resarted and went into the venting cycle for several minutes. The temperature rose and, at one point the boiler seemed to go into the syphon fill program as -//- appeared, but only for a few seconds. The flow temperature is now rising to just over 60C before the green ignition light goes out (roomstat set to 25C, so it's not that turning the boiler off).

Went back to the boiler after about 10 minutes and saw that the syphon filling indicator -//- was showing. This then went out and all that showed was the flow temperature, which rises to about 62 before the boiler turns off. it then drops about 10C before restarting. I then checked parameter 9.C (actual output) which shows 50 when the boiler lights, but drops to 32 and stays there.

So resetting has had no effect. It looks as if there is a problem filling the syphon. Can this be done manually i.e using water from the tap?
 
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So resetting has had no effect. It looks as if there is a problem filling the syphon. Can this be done manually i.e using water from the tap?

Picturing a condensing boiler in my mind (based on assumptions at least!) I'm imagining pouring water through the flue would enter the combustion chamber and subsequently the syphon. Sounds so wrong though (although that's what happens to the condensate) so let someone who knows what they're talking about advise! :D
 
Clambering on the sloping garage roof on a cold Sunday afternoon to pur water down the flue is not high on my to-do list. However, I have found this in the Installation Manual:

To Clean the Condensate Trap
5.1 Pull condensate pipe out of the adaptor.
5.2 Remove trap from boiler.
Clean trap and check that the connection to the heat exchanger is clear.
Fill the condensate trap with approximately 1/4 litre of water and refit in reverse order

So the trap/syphon can be filled without relying on the fill routine
 
CH Temperature Control
When you turn past 6 up to max you can feel a switch operate.

What, exactly, does the switch do?
What happens when you turn the control back, i.e turn the switch off?
 
Spoke to the heating engineer this morning. He couldn't explain what was going on, but wondered if the condensate drain pipe had got blocked again - it is only 22mm plastic all the way from boiler to drain, including going down the side of the house. He couldn't come until Wednesday or Thursday, but we accepted that as the weather was much warmer 5C outside instead of -5C.

During the morning I checked the boiler, as the house was decidedly warmer, and the flow temperature was reading 70C! The hall stat was showing 21C, instead of 19C. So the engineer's suggestion, that the condensate pipe had frozen again, appears to be correct.
 

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