OPOP & Woody: Continually burning and not reaching MAX temperature

[ollielaroo]

Can anyone help here please?

We've had this OPOP pellet boiler for at least 6 years and it's always been running very well.
But the last few weeks it seems to be behaving differently and I don't know why.

Two storey detached house 192sq meters.
UFH and rads upstairs.
OPOP H430 30kw with Woody 5.99E Bio-comfort control panel.
Thermostat at top of buffer tank is set at 60 degrees.
Thermostat at bottom of buffer tank is set at 70 degrees.

The pellet boiler used to ignite automatically when the water in the buffer tank would drop to a certain temperature. The temperature on the boiler would go down to about 25 degrees. It would burn for a couple of hours (or for however long it took to heat the water in the buffer tank) at 100% Power. It would reach at least 79 degrees then it would stop and not come on again for hours or a day or until the next time the water in the buffer tank needed heating up again.

Now it seems the boiler is heating to about 72 or 73 degrees and the Power % starts to dropping down gradually. It's as if the boiler won't continue to burn on full Power 100% and bring the temperature up to nearly 80 degrees like it used to. The auger is dribbling in small amounts of pellets at intervals just as it used to before, but I can't understand why it won't bring the temp up to nearly 80 degrees and stop burning.

Other things I notice:
The pressure gauge on from of the boiler stays up at 3 bar.
The Boiler Temperature (User Setup) is set to 72 degrees.
The pump between the buffer tank and the pellet boiler also seems to be constantly running not sure if that was always the way.

Circumstances that have changed recently:
Not long ago I had to turn the speed of the pump for the rads in the house down from 3 to 1 to try reduce the hissing sound from the rads. Also we had power cuts from recent storms but never caused issues before.

I've been trying to understand the settings available on the control panel.
Very similar to this user manual http://www.kbf.ie/pdfs/nbe_scottemanual_v02.pdf.
I can access the User Setup and the Advanced/Tech Setup.

After cleaning out all the dust from the bottom of the silo and the auger and a delivery of new pellets there is no change. The boiler is still reaching up to 72 or 73 degrees, the auger continues to feed pellets into the boiler and the Power % is gradually going down. Has anyone seen this scenario before?

 

[velvetfoot]

I'd check the things that changed first.

Not long ago I had to turn the speed of the pump for the rads in the house down from 3 to 1 to try reduce the hissing sound from the rads.

How about putting the rads pump back where it was and see if it works the way it used to? Just to eliminate that. Turning it down you would think there is a lower rate of heat removal from the boiler and the boiler would have to turn its output down to match. You have a buffer tank so, I don't think this would be a factor, but it couldn't hurt to try it.

The Boiler Temperature (User Setup) is set to 72 degrees

Was it always 72? It's almost you're getting what you wished for: 72. But if that was the way it always was...

I read in the manual the default boiler temperature is 60, so if you have it at 72 you must have changed it I guess, so my idea that the power cut caused it to revert to default settings is not correct.

You cleaned more than just the silo and auger, right? After owning it 6 years you must have some kind of regular cleaning regime. Could a blocked flue be a factor? I've read that high flue temps are an indication that the boiler needs cleaning.

My boiler modulates down all the time to try to meet the temperature setting.

Your buffer thermostats logic: if top < 60 start boiler and if bottom > 70 stop boiler?

I would think the boiler pump is always running because the bottom thermostat is never satisfied.

Sorry, just fumbling in the dark.

 

[ollielaroo]

velvetfoot,

Fumbling in the dark is as good as anything at the moment thanks .

I've put the rads pump back up to 3 in the house and haven't noticed any change.
As you say we do have a buffer tank so I would agree with you this shouldn't be a factor.

Yes I'm nearly sure the Boiler temperature was always set to 72 since it was comissioned. Also other settings look familiar too. This leads me to think that the power cuts didn't return any settings back to their factory defaults.

At least once a year I give the whole boiler a thorough clean, as well as a minor regular cleaning regime.
When you suggested a "blocked flue" I'm assuming you don't literally mean it could be completely blocked.
As part of the annual clean I reach my arm up as far as I can go with a small brush and sweep the inside of the flue, not that I would get much further up above the height of the bolier. The dust/soot that falls during that cleaning is minimal.

When you say your boiler modulates down all the time are you saying your bolier is behaving as I am expecting mine to?

Yes I think I would agree what you said about the thermostats on the buffer tank
"Your buffer thermostats logic: if top < 60 start boiler and if bottom > 70 stop boiler".

To confirm that I'm not going crazy I've found descriptions in documentation of other brands of pellet boilers of what I'm trying to explain about how our pellet boiler used to work. So here is an example of a description of the behaviour I expect.

***When Stand-by Mode is activated the appliance will go into a cooling mode if the temperature of the water stays a certain amount above the set temperature for a set period of time. When in Cooling Mode the appliance will go through a normal shut down procedure and wait until the temperature of the water drops a certain amount below the set temperature for a set period of time. Once the water temperature is low enough the appliance will automatically go through the full start up procedure and back into Work Mode.***

After spending many hours/days trying to find a user manual for our specific boiler and version of the software in our control box I've only managed to find user guides for more recent models of bolier or for control boxes with a more recent version of the software. Our control box has "Bio-comfort" witten on the front of it and when you turn on the power at the mains/isolator switch on the wall the software name and version on the panel displays "Woody 5.99E". I was told in the past that this version was likely the last interation of the 5 series of the software. Since then I think there has been v6, v7 and v8. It's confusing and frustrating because every time I find and read a user guide for a more recent model of the boiler and version of the software in the control box there are either additional features that are not relevant to what we have and to a non-pellet-boiler-service-engineer it's difficult to know which parameters or settings might really need changing.

As far as temperature sensors go....
One the outlet pipe at the top of the boiler there is a temperature sensor that has always been and still is securely fastened and covered by rounds of insulation tape. I have never tried to remove that so I can't say what that sensor looks like. It is wired back to the control box.
Then there is a sort of pocket on that outlet pipe that has what looks like an insulated copper wire sticking out of it. I believe this goes to the temperature gauge on the front of the boiler.
There is a safety temperature sensor on the back corner of the boiler that shuts off the boier if the temperature goes too high.
We do not have a chimney/flue temperature sensor (Control unit v8 has chimney temperature sensor).

Your last point I also found quite interesting
"I would think the boiler pump is always running because the bottom thermostat is never satisfied".
Hmm maybe I should consider anhother approach like lowering the bottom thermostat on the buffer tank from 70 to 65?

Thanks.

 

[velvetfoot]

When you suggested a "blocked flue" I'm assuming you don't literally mean it could be completely blocked.

Again, just fumbling. Animal, dislodged something or other. You don't brush the flue once a year, from bottom all the way to the outside chimney cap?

When you say your boiler modulates down all the time are you saying your bolier is behaving as I am expecting mine to?

I am currently experimenting with different water temperature set points. If I set mine high, it stays close to 100% power for the entire time like yours, and modulates (powers down) a little towards the end. If I set it lower, it modulates down to 30% and drifts up until it shuts down. The way yours originally worked sounds like my first case, and the way yours is now sounds like the second case.

Hmm maybe I should consider anhother approach like lowering the bottom thermostat on the buffer tank from 70 to 65?

Yes. Even if that works, though, you still wouldn't know what caused the problem. Unless it miraculously cures itself or stops working altogether. It's gotta be one simple thing that's not as it was, not a massive complicated thing.

Thermostat at bottom of buffer tank is set at 70 degrees.

I just had another idea. Maybe it's the bottom thermostat? Does it have a digital readout? Could that have been messed up or the mounting of its sensor gotten loose? The 72 setting of the boiler is pretty close to the 70 setting of the lower buffer tank sensor, I'd think. I know my buffer has some stratification even when loading, so that when it finishes loading, the top is a few degrees warmer than the bottom. That would be all it would take. Maybe the temperature setting readout of the boiler is accurate but for some reason the lower aquastat is never turning off the boiler because it doesn't think it's 70 degrees. Then, indeed, the boiler would modulate down to a lower power output because it's saying "hey, I'm over 72, I'd better back off".

I think your on to something.

 

[ollielaroo]

It seems we have got to the root cause of the problem.

Apparently when the pellet boiler and buffer tank were installed the electrician put in a 'Relay' between the buffer tank and the pellet boiler. Of course I know nothing about Relays, what they do and how they work but I believe it has something to do with how the electricity can managed if you have additional pumps for example. Three electrical wires (from the two thermostats on the tank and the pump that circulates water between the tank and the boiler) are connected in to one side of the box on the wall that houses the Relay. From the other side of the box that houses the Relay the wires then go the Bio-comfort control panel (Woody 5.99E) on the front of the pellet boiler. It seems the Relay isn't working anymore, therefore the pellet boiler wasn't aware of what temperature the thermostats were sensing on the tank and as a result the boiler thought it needed to behave to some extent as if it didn't have a buffer tank.

As soon as I pulled the Relay out from its box on the wall (as suggested by my brother) the pellet boiler could then be governed by the temperature readings from the thermostats on the tank, like it used to do before the Relay malfunctioned. Apparently I just need to buy a new relay for less than €20 and replace the existing one. Even though I've been told the power cuts during the stormy weather some weeks ago shouldn't have affected the Relay it looks like they did in my case.

Many thanks to velvetfoot for the good suggestions and the additional information from kbf.ie.

 

[velvetfoot]

It's a feeling of satisfaction to fix something, and cheaply.
Here's to another 7 years of trouble-free operation!