UFH condensing oil boiler short cycling

[markmorrison1957]

Shall do but will be later - grateful for your helpful comments

 

[markmorrison1957]

There are only 2 pumps! One is on the heating return and is a Wilo - Yonas Pico. It's currently set for large house consuming 75w? but seems to modulate down to 58w!
The supply for the UFH comes off a T pipe from the supply to the upstairs radiators and is pumped round UFH by a Grundfos 25-80 180 set at pump speed 3. No flow measurements show on any pump. The return from UFU is via a T pipe on return from upstairs radiators. Hope that helps figure out are settings OK?

 

[Johntheo5]

On the Wilo, there should be I,II &III, in the middle, with houses to the left and right, is the setting knob pointing to the left or to the right?

 

[Exedon]

Just a quick note in the current Grant boiler range there is no 36/46 the current model is 26/46 and can be taken down to a .75 nozzle.

 

[Johntheo5]

On the Wilo, there should be I,II &III, in the middle, with houses to the left and right, is the setting knob pointing to the left or to the right?

OK, I'm pretty sure that the Wilo is (knob) set pointing to the right, constant pressure, if so, next time its running, turn the knob almost fully anticlockwise, (proportional pressure) as you are turning it you will see the pressure setting changing, (it can be set incrementally in 0.1M steps), keep adjusting it until you get 6.0M, note the power in watts, see does the noise abate, the newer versions of these pumps also display the flowrate in m3/hr. have a look out for it.

 

[markmorrison1957]

Wilo was pointing to right but to Number 3 setting!!

 

[markmorrison1957]

I'll fiddle with pump in the morning and I'll check with Grant again re lowest nozzle size but I'm sure it says on top of boiler 36-46 but again - will have a look in the morning!

 

[Johntheo5]

Wilo was pointing to right but to Number 3 setting!!

I thought you said it was set to your large house!!, OK, just try it as I suggested above, you are trying to get it to satisfy both a very small flowrate on UFH only and a fairly high flowrate on rads, these are a fabulous pump with all those incremental settings.

 

[markmorrison1957]

I'll let you know how the pump fiddling works! It does appear to be, according to metal plate on top of my boiler, that it is a Grant Boilerhouse 36 - 46 factory fitted with a 1.25 nozzle giving out 41kw. A 1.00 nozzle will reduce this to 36kw. The Riello burner on the boiler is RDB 2.2BX (V36-46). Perhaps could you consider is it possible to replace with a smaller powered RDB BX (V26 -36)? Would the smaller powered burner fit?

 

[markmorrison1957]

Sorry - the Grant boilerhouse manuals (online and paper copy) show different factory fitting nozzles so mine could be 1.1 or 1.25! Also, the online manual (UK rev July 22) does say it's a 26-46 though the boiler top plate says 36-46! The manual that accompanied the boiler is IRL June 23 shows model 26-36 and 36-46. Boiler dimensions for both are the same. The burner manual (10/22) that came with boiler shows RDB 2.2 BX V26/46. I think I need to go and look at burner or phone Grant because as previous post I could go for a 0.75 nozzle! Please try to ignore this ranting as I suffering confusion with online and paper manuals. Maybe different countries of manufacture!!

 

[markmorrison1957]

Further apologies - Commissioning Passport by Engineer shows burner to be RDB 2.2BX v26-46!! Night night now!

 

[Johntheo5]

There should be a label on the actual burner giving the product number, I can't find any reference to a 26/46, I see a V26/36 & V36/46 and would be surprised if a simple nozzle down sizing without changing the blast tube could reduce the output from 46 to 26kw.

 

[markmorrison1957]

I checked the burner in my garage and it efforts says RDB 2.2BX V26-46!
Turned Wilo pump dial on the return to the boiler anticlockwise until it showed 6.0.
The wattage ranges from 49w to 61w.
The boiler has been firing for nearly 2 hours on UFH only and is now firing on for 2-3 minutes (5min one time) and is off for just over1 min - the firing time has lengthened! Manifold shows water in at 50c and return at 45c. What do you think? Oh, extremely grateful for your time and help!!

 

[markmorrison1957]

Oh, the dial on the Wilo pump is on the left at image of middle sized house

 

[Johntheo5]

I checked the burner in my garage and it efforts says RDB 2.2BX V26-46!
Turned Wilo pump dial on the return to the boiler anticlockwise until it showed 6.0.
The wattage ranges from 49w to 61w.
The boiler has been firing for nearly 2 hours on UFH only and is now firing on for 2-3 minutes (5min one time) and is off for just over1 min - the firing time has lengthened! Manifold shows water in at 50c and return at 45c. What do you think? Oh, extremely grateful for your time and help!!

Afraid that makes little or no sense thermodynamically.
Just say its firing for 3 mins and off for 1 min, then boiler output is 41*3/4, 30.75kw, even though the off time based on that output seems to match up. If the UFH was the only user (what about HW cylinder??, was this off) then the UFH manifold circulation has to be 30.75*860/60/5, 88.15LPM, or 88.15/12, 7.34LPM/loop?, highly unlikely and the boiler circ rate, 88.15*(50-45)/(65-45), 22.03LPM.

So, suggest we "forget" that for the moment and set the Wilo to speed II which I think shows up as C2? and take another set of readings sometime, maybe no harm also to take a set of readings, cycle times and pump power while heating the cylinder only.

Oh, the dial on the Wilo pump is on the left at image of middle sized house

Just to explain those Wilo modes.

The I,II&III, (C1,C2&C3) are just the same as the old 3 speed pump settings (now known as constant curve) , (C1=3.2M, C2=5.6M, & C3=7.5M), the houses to the left are all proportonal pressure, PP settings, and as the flow increases the pump pressure increases, the houses to the right are all constant pressure, CP settings, and the pump will maintain whatever pressure (in M) that you care to set it to.