Vaillant condensing boiler freezing - minimising condensate?

BooJewels

I woke this morning to a quiet and cold house, as the heating wasn't running and the rads were cold.  Having experienced it before and it being -5°C overnight, I hoped it was just a frozen condensate pipe - which it was.  A few jugs of warm water later, I was able to restart the Vaillant boiler and it has run fine through the day.

Around 6pm it seemed to be making a lot of noise, so checking it, it was making wet gurgling sounds, then stopped and I got an F.29 error/fault code.  I repeated the warm water routine and it's still running, although the house has struggled to get warm today - it obviously got very cold overnight where the boiler would normally have fired up below 15°C - it was 13.1°C in the house when I got up - it's still only 16.6°C - thermostat in an evening is set to 18.5°C.

I don't understand how condensing boilers work, but read somewhere that they produce less condensate at higher boiler temperatures - but that's less efficient/more expensive.  So that I don't have a problem overnight, would it reduce the volume of condensate produced if I temporarily raise the temperature overnight during this wee cold snap?  I think it's currently set at 60°C.

I'm actually surprised that it froze again during the day as I calculate the external vertical drain pipe to be about 680 cubic cm (32mm dia x 1500mm high - if my maths is right - it sounds plausible) - that's more than 2 drink cans worth - I thought it only dripped out?

TimeLord1

YouTube, you should find a fix. I had an error code. It's an ignition issue normally caused through burst of cold water being pumped into hot running hot water, and turning the pump up can help. But resetting should start it.

BooJewels

Thanks for the suggestion - I already did that step at 08:00am when I woke to no heating.  That error code was F.28 - which is an ignition issue and one of the most common causes is a frozen external condensate pipe. Hence me pouring several pints of warm water down the outside of the condensate drain pipe to unfreeze it, then successfully re-starting the boiler - which ran fine until 6pm.

What I was actually asking was whether a higher boiler temperature would reduce the volume of condensate produced and thereby reducing the probability of a further freeze stopping the boiler overnight?

TimeLord1

If your gas pipe outside and is visible ie running up a wall you can get some insulation foam tubing. If you see a good glow on the ignition and if it looks a bit worn by usage might be worth getting it replaced or cleaned out.

Yes, increasing your boiler flow temperature will reduce the amount of condensate produced, which in turn reduces the risk of the external pipe freezing again tonight. So you can well should be in winter mode level 

TimeLord1

https://www.gassaferegister.co.uk/media/2770/customer-information-frozen-boiler-condensate-discharge-pipes.pdf

TimeLord1

Some causes are the angle of the pipes too straight and some vents not sealed watertight, and it freezes it. Silicone around those if it's possible.

WIAWSNB

BooJewels said:

I woke this morning to a quiet and cold house, as the heating wasn't running and the rads were cold.  Having experienced it before and it being -5°C overnight, I hoped it was just a frozen condensate pipe - which it was.  A few jugs of warm water later, I was able to restart the Vaillant boiler and it has run fine through the day.

I don't understand how condensing boilers work, but read somewhere that they produce less condensate at higher boiler temperatures - but that's less efficient/more expensive.  So that I don't have a problem overnight, would it reduce the volume of condensate produced if I temporarily raise the temperature overnight during this wee cold snap?  I think it's currently set at 60°C.

Interesting! Yes, a higher flow temp will mean a higher return temp, which means less condensate produced. And the cond produced will likely be slightly warmer, so even less chance of freezing. 

But, the real issue is almost certainly caused by the external condensate pipe either not flowing quickly enough, or not being insulated, or both. Any chance of a photo? I'm sure you'd prefer to have the actual cause sorted?

BooJewels

Thanks for the assorted posts @TimeLord1 - clearly at 11pm, there's a limit to what I can achieve - I can't buy or fit insulation or apply silicone. I was a bit confused about the gas pipe outside bit - the condensate drain pipe is outside - but I think all the gas supply pipes are inside, from the meter that is below the boiler.   I can't see the igniter, so have no idea how that is looking or what it should even look like.

The condensate drain pipe comes out below the boiler at about 5 foot high, then straight out through the external wall and drops to a drain at ground level - no bends, angles or slopes, just a vertical drop of a bit over 5 foot outside.

All I can do tonight is warm the drain pipe again before bed and raise the boiler temperature, if that might reduce the condensate produced. I've already increased the overnight temperature on the thermostat, so that it should tick over overnight without getting too cold.  Hopefully it will warm up tomorrow and I can then address better long term solutions.  Although in fairness, I don't think it's done it for 2 years, so it's not been this cold that often.

BooJewels

WIAWSNB said:

BooJewels said:

I woke this morning to a quiet and cold house, as the heating wasn't running and the rads were cold.  Having experienced it before and it being -5°C overnight, I hoped it was just a frozen condensate pipe - which it was.  A few jugs of warm water later, I was able to restart the Vaillant boiler and it has run fine through the day.

I don't understand how condensing boilers work, but read somewhere that they produce less condensate at higher boiler temperatures - but that's less efficient/more expensive.  So that I don't have a problem overnight, would it reduce the volume of condensate produced if I temporarily raise the temperature overnight during this wee cold snap?  I think it's currently set at 60°C.

Interesting! Yes, a higher flow temp will mean a higher return temp, which means less condensate produced. And the cond produced will likely be slightly warmer, so even less chance of freezing. 

But, the real issue is almost certainly caused by the external condensate pipe either not flowing quickly enough, or not being insulated, or both. Any chance of a photo? I'm sure you'd prefer to have the actual cause sorted?

As described in my most recent post, the condensate drain is just an external plastic pipe that drops vertically from where it comes out through the wall to a grid at ground level.  No bends, slopes or angles.  No idea really how it has managed to freeze - it feels like it has more than enough capacity to cope with the volume of water I would anticipate passes through it.  It's not insulated - it's against an old stone wall that undulates quite a lot, so tubular lagging couldn't cover it all efficiently.  No chance of a photo tonight I'm afraid - maybe tomorrow. 

But I will be asking the BG service people who cover my CH to look at a better solution for me going forwards - probably not covered by my service contract, but I don't mind paying to avoid this in future.

grumpy_codger

Sometimes it can be easy to disconnect the (white plastic) condensate pipe near the boiler and to collect the condensate temporally to a bucket (that you'll have to empty regularly)

BooJewels

grumpy_codger said:

Sometimes it can be easy to disconnect the (white plastic) condensate pipe near the boiler and to collect the condensate temporally to a bucket (that you'll have to empty regularly)

That's actually one of the solutions I was considering - I gave it a test pull to see how tight the fitting was, to see if I could bypass the external bit - but it felt tighter than I was prepared to risk - and it's high enough that I'd need to source the right size of hose to join to it etc.  But one of the future options I might have suggested was a switchable valve at that junction, so I could use a hose on it when very cold outside.