Boiler Pump keeps running non-stop Saunier Duval THEMA NOx F 25

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I’ve have this boiler which was in place when I purchased my property and have some issues with it.
I think this is the model, it's on the rear of the control panel, but no model number anywhere else on the boiler as far as I can see!
valve water leaked from.jpg Control unit.jpg

I can’t find an exact manual match.

It stopped working over the weekend, no heat or hot water. This I’ll explain below.
LCD on boiler was flashing "F 29"

The other issue is the pump will not turn off if I set boiler for Hot water and Heating.
If I set boiler for Hot water only then the pump stops.
Holiday mode also pump stops.

Even with temperature valve and cut off valve on radiator the pump still keep running.
Due to the position of the boiler it’s not practical to keep going and changing the setting manually.
Over weekend I had no hot water.
Checked boiler and was showing .3 Bar
When I put boiler in Hot water and Heating mode I then had heating and hot water I taps etc!
I then bled a small amount of air out of the radiator.
Then the boiler would not run at all, no heating or hot water.
I then re-pressurised with water to 1.5 Bar turning off valve as soon as it reached that setting.
Then boiler kicked in, suddenly LCD was showing 2.5 bar.
Some water dripped from I think a valve with red top!

I drained/bled water off the radiator, about 1.5 L of water.

Got bar reading down to 1.5 bar.

I now can get hot water with only hot water only setting or heating and hot water setting.

When I turn on the setting to heating with the one radiator I have isolated, with both valves shut the boiler still fired up for a few minutes.

Then when boiler shuts off the pump remains running, never stops!

If I leave in Hot water only setting the pump turns on from 10 seconds to 30 minutes at random all times of day and night.

It seems to do this for longer and more often in winter, and less often and less time running as weather gets warmer.

I can’t see any more dripping from underneath boiler, no obvious leaks from radiator, but maybe there is a very slow one.

I can see however the boiler has dropped to 1.4 bar last night, this morning now 1.3 Bar.

Can anyone point me to what part is faulty in regards to pump keeps running non-stop?

One other thing I’ve noticed with boiler is it tends to change temperature when having a shower, but is this the fault of the shower head, flow too restricted etc?

Thanks for any info on this crappy boiler.
 

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Update.
My boiler isn't firing up now.
Error code F28 flashing.

When I turn the boiler on I can hear the pump running, the exhaust is running, but the water temp on the display doesn't increase.
No hot water at the taps, no heating.

After a few minutes I can hear what sounds like the boiler trying to light, sounds like a ticking, I assume electrode sparking, it does this a few times and then shuts down with the F28 error and red light flashing.
It's been running ok for three months, not perfect but ok, as per my previous post.

Normally powering off and on again would fix this problem when it happened a few times before, but now it's dead.
Any info on what might be wrong would be appreciated.
 
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I had a couple of these on my books for a few years that brought untold misery to me and their owners.
Fortunately, both boilers became terminally ill last year and ended up in the skip.
I suggest you prepare yourself for that scenario.
 
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Thanks for the reply.

Doesn't sound good news then. I found a long list of possible issues under that error code online, sort of take your pick.

I've checked most of the electrical connections I could remove, some I couldn't, no space to get your hand inside this thing.
It all looks mostly very clean, apart from one pipe with a very small leak. It took 3 months to lose .3 Bar, so little it doesn't drip anything into a bucket.

What I did find recently was a box with a part that has been replaced, photo attached.
It looks the same but one electrical connection is facing a different way. The voltages don't seem to be the same!! Was this a botch repair I wonder, or maybe original part no available! Photos attached.
One thing I didn't mention, I'm in the sticks, so I run this thing off gas bottles. Is it possible water, air or dirt from the bottle has entered the boiler in some way causing this issue?
It was very near the end of the gas bottle when this happened!
IMG_20220408_171947 gas.jpg IMG_20220408_172004 gas fitted.jpg IMG_20220408_172931 boiler.jpg IMG_20220408_172947 leak.jpg
 
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