Grant boiler rusting inside after 1 yr

[RayPlumb]

I have a clients oil Grant boiler I fitted last year. It is a Vortex pro 26-46 system.
It is just a small system loop as it is a pool boiler. Heated through a heat exchanger directly behind the boiler.
I went to service today and took about a handful of rust off the baffles. There was even signs of rust on 2 of the chamber door nuts.
Boiler has a 150mm vertical flue about 2.6mtrs located in a pool pump house with all pool chemicals.!.. First thought on the rusty nuts was the pool chemicals in the air. But this does not explain the rusting baffles. Could this be result of a blocked condensate or flue fault.
I then done a combustion test and all spot on .
Any advice and ideas where to check appreciated .

 

[ShaunCorbs]

What’s the return temp ?

 

[RayPlumb]

What’s the return temp ?

Didn't measure it today . pipes hot enough, hot to touch. What would be a bad temp.

 

[ShaunCorbs]

Didn't measure it today . pipes hot enough, hot to touch. What would be a bad temp.

Anything below 50

 

[RayPlumb]

It does run in condensing mode for quite a while, which I presumed a good thing. M I says ''To ensure maximum efficiency, the boiler return temperature should be 55°C or less, this will enable the latent heat to be condensed out of the flue gases.''
If running in this mode for too long would this then be a bad thing?
The initial set up had a temp difference of 14deg. I would have recorded flow and return temp but probably on the bench mark which would be left on site.

 

[RayPlumb]

weird thing is there is also rust forming on the underside of the metal plate the expansion vessel sits on just above the burner, and some green oxidization on the copper fire valve sensor..
No leaks as pressure at 1 bar where I left it last year.

 

[RayPlumb]

The boiler is in frost protection mode and pool side off in winter. It was installed in mid summer so maybe got to temp quite quick. But in few months either side of this it would be much cooler and take a lot longer to heat up hence a lower return temp for longer. Im going to try get back and measure today.
How long would you give it before testing return temp. ?
If return still below 50deg would a manual bypass be the answer ?

 

[RayPlumb]

Anything below 50

Hi Shaun
Went out today to test and the boiler had been running so allowed to cool down. The pool heat exchanger was showing pool water already at 25deg .
So started the boiler at -
1.40pm and T1 Flow - 28degC T2 Return - 25degC
1.47pm T1 flow - 44.4 deg , T2 return 35.6deg , diff 8deg
1.50pm Flow - 61.5deg , Ret 48.0 , diff 13.5deg
1.55 F - 66.6 d , R - 51.3 d, diff 15.3deg
2.05 F - 70.8 d , R - 55.8 d , diff 15deg
Then roughly levels out , slowly creeps up only 1 deg to 71.7d - 56.2deg over the next 50 min.
So it took roughly 7 min to get up to 40 deg return temp and another 7min to get to return of 50 deg.
Saying that if the pool temp was 15 deg a few days ago probably take longer to heat up?

 

[ShaunCorbs]

Yep correct or bigger difference eg dt I suspect that’s your problem

And the pool filter / equipment is in a different room etc

 

[RayPlumb]

Yep correct or bigger difference eg dt I suspect that’s your problem

And the pool filter / equipment is in a different room etc

No the pool filter /equipment is right next to it a foot away.
All quite compact . I have 28mm flow out the boiler, about 60cm reduce to 3/4''into a Bowman pool 76kw heat exchanger. Then out heat Heat Ex. about 20cm into a 28mm Mag Filter - 30cm into the boiler.

 

[RayPlumb]

I'm going to go tomorrow to switch it off for a few days for pool to cool down. Then see how long return stays below 40/50 deg until up to safe temp. At the moment the flue temp is only just reaching the 80deg after an hour.
What would you suggest ... I could up the output from 41kw to 46kw..?
Squeeze in some kind of bypass??