Firebird Condensing boiler issues

Sheryl1971

I have a C35 condensing boiler operating 1 manifolds around 18 kw, 1 manifold around 11kw, 11 radiators, 4 towel rails & trench heating. My issues are as follows

1: Boiler overheats

2: Boiler struggles to get to set point and if finally reaches set point, flow will increase by 10C

3: Boiler cycles on and off every 2 mins

4: Boiler blows water out the condensate pipe, dries out the trap and melts the condensate pipe.

5: On the flue analyser the settings are as follows: Danfoss nozzle .65 80S, 12 Bar, Air 5, CO2 12% flue gases 134C, excess air 43%.

Can anyone help me as to what is causing all these issues please. UFH manifolds run 80% of the time there is no buffer tank of LLH on the system.

Lenar3556

Is there any sooting up within the boiler? 12% CO2 on that boiler might be a bit high. Is it a Riello burner or Elco?

Most of your issues point towards circulation problems. So that would need to be assessed - Is circulation pump working correctly. Are any zone valves opening when they should. Is there operative interlock between the boiler and zones using the auxiliary switching on zone valves? The sudden temp change could be the result of blending valves for UFH operating.

First action might be to reduce the firing rate down to the minimum 26kw as a first step. Is this a new house?

Sheryl1971

Hi, thanks for your reply. It is a riello burner, i have enquired about swapping it for a Elco burner to see if that would help. Yes there is sooting in the boiler and just now I have noticed the condensate water that is getting blown out the trap is black. Circ pump seems to be working correctly, as the other manifold which is 50 meters from the boiler and the rads are all operating correctly. All zone valves seem to be opening correctly.

I wondered if we should down rate the boiler, but after seeing the black water discharge tonight, maybe the heat exchanger has been damaged.

Wearb

Most likely it has at least a couple of badly damaged baffles. Was it serviced recently?

Lenar3556

https://www.boards.ie/discussion/comment/122225553#Comment_122225553

Doubtful it’s damaged, just running sooty. The Riello burner doesn’t have the post purge function, and to be honest the downfiring arrangement itself was in my view somewhat illconceived.

Suggest clean it all out as best you can. Change nozzle for 0.6 80ES (should be circa 26KW at 12bar pump pressure) and adjust air to give you 11.3% CO2. That should help.

Corrected - 80deg nozzle

Sheryl1971

Thanks for your reply and advice, very much appreciated. The boiler has been serviced recently and baffles looked ok. The boiler was also cleaned throughly. I will speak to the plumber tomorrow and ask him to change the nozzle. Hopefully this will help the condensate trap blowing, fuel consumption and sooting. The plumber thinks the flue is not letting enough air in, Do you know if the 150mm flue fits the C35?

Lenar3556

https://www.boards.ie/discussion/comment/122226024#Comment_122226024

certainly worth checking too. Some were a poor fit from the factory even.

Sheryl1971

Here are some images of the baffles, melted condensate drain hose and the front door panel. Some did say to cut the corners to allowed better heat distribution.

Wearb

12 bar isn't allowed when burning kerosene.

Do you have a pic of the back end of the baffles. What we've seen in that photo isn't too bad.

How old is that boiler? Does it have a stainless steel trap?

jimf

if that boiler is a c35 silver 130 would not be far off the running temp

nozzle on that originally would have been a 85x80es at about 9bar

drop that to 75x80es and increase the pressure to 9.5bar under no circumstances have the co2 above 11.3% or have a s nozzle fitted

get those baffles sorted replace hose to condensate trap is the trap a plastic or stainless steel

door gasket is not too bad in can be flipped over for another use

just to comment on your original post whoever was at your boiler and left it with those settings needs to go away for a bit of boiler training 12bar with kerosene is a no no no wonder your hoses are burning off

jimf

where are you living maybe somebody on here may be in your area to help out

Sheryl1971

Hi there

The boiler is 4 years old. I live in NZ. The reason I’m asking on this board is because you guys are so knowledgeable in boilers compared to our tradies in NZ, there’s not a lot of understanding about Central Heating here, the set it all on high and walk away.

The boiler is run on diesel, it’s a C35 condensing boiler. Original nozzle was a .65 80s and still is this nozzle, with a horizontal flue.

Wearb

Post a few pictures of any labels on the boiler and burner. Also a few overall pictures.

Those boilers would not be allowed to run on diesel here, especially with a horizontal flue, which is a low level flue.

Lenar3556

https://www.boards.ie/discussion/comment/122228808#Comment_122228808

You could go to 13.5 bar for diesel, higher fuel pressures have been a factor in getting cleaner burning on that particular boiler. We wouldn’t usually run condensing boilers on diesel in Ireland, but I gather it is common on the continent.

In that case I would suggest maybe a 0.55 80S nozzle at 13.5 bar. The CO2 is the big one here, it was set too high. The boiler needs additional air to get the CO2 down to about 11.3%. Reassess any water circulation issue when the boiler is running correctly.

Sheryl1971

Thanks everyone for your replies. Some photos attached. This system has another expansion vessel in the hot water cupboard, should this be nearer the boiler?

Wearb

I'd advise setting up as advised in Lenar's last post, if you have difficulty getting kerosene. Otherwise get kerosene and set it up for that.

Flue should be 100mm internally.

Re on off every 2 minutes. Is it cutting out on thermostat or locking out and restarting?

Check for combustion products in air intake. Remove flapper in air intake.

Sheryl1971

hi there

Thank you for your advise. We don’t have kerosene in NZ. The flue is 125mm outer diameter. Cutting out on boiler thermostat. Our air intake does not have a flap on it. I will set up as per Lenar’s post and see what happens.

Wearb

You have a circulation problem if it's running on such a short cycle. Set it up properly and then see if it's still short cycling as much.

Have a look at the manual for the position of the flap mentioned.

Sheryl1971

it short cycles the most on the UFH 10 zone manifold which is approx 15m away from the boiler. If it shorts cycles does it mean not enough flow through the boiler or to much?

I have checked the manual and there is no flap on our boiler at all. The plumber is saying we need more air in the boiler but the air damper is set for the CO2 settings.

Sheryl1971

another question, we have an additional expansion vessel on our invented HWC, can this also be used for addition expansion for the boiler even though it is at the end of the system 15m away from the boiler?

Wearb

https://www.boards.ie/discussion/comment/122233038#Comment_122233038

It's not that simple re flow, but not enough will cause shortcycling. But that zone might not have enough demand for the boiler output, so would need further plumbing such as lowloss header or buffer. A good plumber should be able to quickly recognise that flow problem.

Re not enough air. If you adjust boiler for air as discussed above, than that's the end of that argument. Your tech doesn't seem to have a good understanding of combustion.

Sheryl1971

Thanks Wearb. I have discussed a LLH with him and now he thinks its a good idea. Re combustion, he thinks the flue is not suited for the boiler but i argued that those flues are on a lot of firebird boilers worldwide.

I have now opened a radiator zone when the manifold is running to try and overcome the flow issue. Thank you for your advise and help.

The nightmare continues :-))

Dtp1979

https://www.boards.ie/discussion/comment/122228808#Comment_122228808

I wouldnt bring a firebird from one side of Laois to the other and here’s you bring one to to the far side of the world.
I haven’t really followed the thread so apologies if I missed something.
35kw is too big to run a small circuit. That’s why it’s short cycling. Not sure if them boilers are really suited to diesel. They’re hard enough to get working properly on kero

Dtp1979

Trying to quote for the unvented vessel comment. Answer is no they’re separate systems

Sheryl1971

Hi there, I thought they are two different systems as well, but my heating man seems to think we can use it for the extra expansion vessel needed for the boiler. 🤷‍♀️ These firebird boiler are everywhere over here. Our big central heating company uses them everywhere.