Central Heating Pitching - Any Advice

slash2000

Hi all,

My woodstove (boiler) will pitching when I run both the central heating and woodstove together. It stops when I switch the central heating off.
They can both run fine on their own but not together.

I've attach a sketch of my heating layout (vent,expansion,pumps left out for clarity)

Any suggestions what could be causing it?

Thanks

John.G

slash2000 wrote: »

Hi all,

My woodstove (boiler) will pitching when I run both the central heating and woodstove together. It stops when I switch the central heating off.
They can both run fine on their own but not together.

I've attach a sketch of my heating layout (vent,expansion,pumps left out for clarity)

Any suggestions what could be causing it?

Thanks

The positioning of pumps and vents play a big part in pitching problems.
This is how FAS suggest it should be done, see page 39 of attachment.

slash2000

John.G wrote: »

The positioning of pumps and vents play a big part in pitching problems.
This is how FAS suggest it should be done, see page 39 of attachment.

Thanks John - very useful document.

I've updated my sketch to show the pumps and expansion pipe.

Any suggestions?

John.G

slash2000 wrote: »

Thanks John - very useful document.

I've updated my sketch to show the pumps and expansion pipe.

Any suggestions?

Combining these systems can be a complete minefield and highly dangerous if not done properly, its very difficult to get a definitive layout but there are plenty of wrong ways of doing it!.
I wouldn't be happy personally with one combined vent, each should have its own as well as a separate cold feed&expansion pipe.

There are numerous posts on here re combining the systems, have a trawl through them, they may be of some help but the best advise I will offer is to get someone who is thoroughly familiar with these systems because of the potential dangers involved.

slash2000

Thanks again John
I did have a separate vent for the oil boiler side but my plumber removed it when I got him to do a bit of work on the system - it worked fine for a while but began to pitch after I replaced the oil boiler pump. I'll get my plumber to take another look at it.

John.G

slash2000 wrote: »

Thanks again John
I did have a separate vent for the oil boiler side but my plumber removed it when I got him to do a bit of work on the system - it worked fine for a while but began to pitch after I replaced the oil boiler pump. I'll get my plumber to take another look at it.

That's interesting that the pitching started when the oil boiler circ pump was replaced, can you see its make/model, it may have been replaced with a higher head pump, long ago these pumps had 3 speed settings so you got a certain form of control by selecting one of the settings. Today only the higher efficiency pumps are available but they are also pretty smart in that, depending on the manufacturer, you can select a number of different heads and then in that mode the pump will maintain that head even when the circulating flow reduces, if the other mode is selected then you can again select one of a number of heads and put the pump to variable pressure (head) control but in this mode the pump will automatically reduce the head (by speed control) as the flow rate reduces. When your two systems are on together then you more or less have two pumps now feeding one system so each pump head requirement is very much reduced and with fixed speed or constant head control the pump(s) head is too high and you can get pitching.
IF you have one of these smart pumps on the oil boiler then you can try running it in the variable head mode and it could well stop the pitching.
Anyway see what type of pump was retrofitted and that will tell a lot especially since you didn't get pitching with the old one as it was probably a lower head pump.

Edit: You might look at the solid fuel pump as well, make/model and see what the speed setting is, assuming its a standard 3 speed, that will tell us a bit more by looking at its pump curve.

slash2000

The old pump was a Tuscon, it seemed very basic- no speed settings. I replaced it with a Grundfoss UPS2, it has three speed settings, which is currently set to 1(lowest). That's a good point about the head, I'll dig up the specs for both pumps.

slash2000

slash2000 wrote: »

The old pump was a Tuscon, it seemed very basic- no speed settings. I replaced it with a Grundfoss UPS2, it has three speed settings, which is currently set to 1(lowest). That's a good point about the head, I'll dig up the specs for both pumps.

Edit: I not sure of the make of the woodstove pump but it looks pretty old, I don't think it has any speed settings. It could be a case of the new oil boiler pump is too strong for the old wood stove pump.

John.G

slash2000 wrote: »

Edit: I not sure of the make of the woodstove pump but it looks pretty old, I don't think it has any speed settings. It could be a case of the new oil boiler pump is too strong for the old wood stove pump.

Thanks, can you confirm that this is the Grundfos type (smart) you have please.

https://ie.grundfos.com/products/find-product/ups2.html

slash2000

John.G wrote: »

slash2000 wrote: »

Edit: I not sure of the make of the woodstove pump but it looks pretty old, I don't think it has any speed settings. It could be a case of the new oil boiler pump is too strong for the old wood stove pump.

Thanks, can you confirm that this is the Grundfos type (smart) you have please.

https://ie.grundfos.com/products/find-product/ups2.html

Hi John, yes that is the pump I have. Although I don't think it's a smart pump - it just has three speed settings.

John.G

slash2000 wrote: »

Hi John, yes that is the pump I have. Although I don't think it's a smart pump - it just has three speed settings.

Has it the three green LEDs as per attachment and a selector switch/button? and can you give the exact model as per label.

I am pretty sure that you have this model, I have attached the users manual for changing operating modes which is very very easy.
If you change from fixed speed mode to variable (proportional) head mode then according to the pump curves.... Speed 1 selected
10 LPM = 3.5M head fixed speed and 1.3M proportional control
15 LPM = 2.9M head fixed speed and 1.6M proportional control
20 LPM = 2.5M head fixed speed and 1.8M proportional control

As you can see there is a very big difference in the the head pressures at the lower flow rates and probably give enough head pressure if the oil fired boiler was running on its own, I would certainly try it on proportional control and see how you get on.
I will edit this post very soon and include the link for the users manual.


https://ydrometal.gr/wp-content/uploads/2018/02/Grundfos_ups2_Manual.pdf

Edit Again: Sorry for any confusion but yes there was a UPS2 I think with 3 speed control only, if so then you can't really do any more to get the head down.

slash2000

It's a relatively new pump (last year) so it may have proportional control. I'll get a look at it tomorrow and switch it over if possible. I'll report back.

esox28

hi. op were are your non-return valve located can you mark them up on on your sketch.

slash2000

esox28 wrote: »

hi. op were are your non-return valve located can you mark them up on on your sketch.

Hi esox28, I have two non return valves after each pump.
I've updated the sketch.

slash2000

@ John.G

I checked my pump and it turns out I do in fact have the pump with proportional control! I set the pump to No1 proportional control and ran both systems and so far no pitching!!!:)

I'll try it out a few more time this week and report back.

Thanks for the advice John.G.....I owe you a few pints!!

John.G

slash2000 wrote: »

@ John.G

I checked my pump and it turns out I do in fact have the pump with proportional control! I set the pump to No1 proportional control and ran both systems and so far no pitching!!!:)

I'll try it out a few more time this week and report back.

Thanks for the advice John.G.....I owe you a few pints!!

That's good news, it will be very interesting to see how that setting (1) performs with the oil fired boiler only in service, keep a eye on the temperature difference between the boiler flow and return as you will now have a reduced flow through it and if its a condensing boiler I know that there is a minimum return temperature specified by the different manufacturers to avoid corrosion.
If too low then you have the option of changing to prop.setting 2 (or 3) as long as these settings don,t cause pitching with both system in use or you could leave the setting as is and raise the boiler stat set point to ensure the return temperature is above the specified minimum.
Keep us informed as all this was very interesting.

slash2000

John.G wrote: »

That's good news, it will be very interesting to see how that setting (1) performs with the oil fired boiler only in service, keep a eye on the temperature difference between the boiler flow and return as you will now have a reduced flow through it and if its a condensing boiler I know that there is a minimum return temperature specified by the different manufacturers to avoid corrosion.
If too low then you have the option of changing to prop.setting 2 (or 3) as long as these settings don,t cause pitching with both system in use or you could leave the setting as is and raise the boiler stat set point to ensure the return temperature is above the specified minimum.
Keep us informed as all this was very interesting.

Thanks John, good advice as always. It's a condensing boiler I have. I've checked with the manufacturer and they recommend a return temperature of 45 degrees. I'll monitor it this week and keep you posted.