Water heating pump keeps air locking

[Beardyoldman]

Hi there
First post so hope I’m on the right forum!
Anyhow I have an oil fired Worcester boiler approx 13 years old . Heating system open vented is original about 30 years old micro bore pipes.
Feed from boiler 28mm has manual bleed valve then splits into two 22mm pipe ...lower into Grundfos UPS2 15-50/60 130 pump goes to radiator circuit. Other higher pipe into Grundfos UPS2 15-50/60 130 pump which goes to heat water cylinder upstairs (2 storey detached )
Problem is with the upper pump continually needing bleeding as it air locks and stops water heating. Has been an on going problem for some time so wondering whether a automatic air bleed to replace the manual one and also a magna clean filter would help?

 

[snowhead]

First, both the pumps need levelling up so the shaft is horizontal.
That will probably mean removing the head and twisting the body so the connection box is to the side or up, AS per Grundfos instructions, pic below.

That will stop some of the air.
As well as that on the top pipe between the pump and wall where the elbow is, remove that and fit a Tee and auto air vent there.

 

[SJB060685]

I believe the short pipework from boiler pumps is under negative pressure, assuming the vent and cold feed go into boiler right hand side trappings. Can you rule out air being drawn in through leaky valves between boiler and pumps? As Snowhead says pump should be installed to manufacturers guidelines. It might be worth putting an AAV or manual air vent on short piece of pipe tee'd off of cylinder flow inlet as well.

 

[Beardyoldman]

Hi Snowhead
Thank you for replyi

First, both the pumps need levelling up so the shaft is horizontal.
That will probably mean removing the head and twisting the body so the connection box is to the side or up, AS per Grundfos instructions, pic below.

That will stop some of the air.
As well as that on the top pipe between the pump and wall where the elbow is, remove that and fit a Tee and auto air vent there.

View attachment 41968View attachment 41969View attachment 41970

Hi Snowhead Thankyou for replying
and apologies for the delay coming back . If I understand you correctly I can change the head of the pumps by undoing the Allen key bolts and turning the head 90 degrees? Also fitting an AAV on flow pipe leading into heating pump..? Will that not risk air being drawn into system? If not any particular type of AAV you would recommend? Thanks
[automerge]1577128526[/automerge]

I believe the short pipework from boiler pumps is under negative pressure, assuming the vent and cold feed go into boiler right hand side trappings. Can you rule out air being drawn in through leaky valves between boiler and pumps? As Snowhead says pump should be installed to manufacturers guidelines. It might be worth putting an AAV or manual air vent on short piece of pipe tee'd off of cylinder flow inlet as well.

Hi SJB
Thanks for you reply.

I did wonder whether air might be drawn in through the old manual air vent on the flow from the boiler to the pumps? as I read somewhere that you shouldn’t have a air vent on the flow into the pump ! Not sure how I would check if this is what’s happening? Would I be better replacing the old manual vent with an automatic one?
Also I take it you mean fitting another AAV on the flow pipe going into the heat exchanger on the copper cylinder?
Thanks

 

[SJB060685]

That short piece of pipework is only under negative pressure when the pump/pumps are energised, if its drawing in air then it might be seeping water out when the pumps and boiler aren't running, check to see if damp.
Do you know how high above the pumps the header tank is? I doubt its cavitation but thought I'd ask.
Yes I would put a manual air vent near the cylinder and possibly remove the one near pumps.
Also out of curiosity do you know how that system is wired with two pumps? Do you only get heating when hot water is on or is the a relay somewhere?

 

[Beardyoldman]

That short piece of pipework is only under negative pressure when the pump/pumps are energised, if its drawing in air then it might be seeping water out when the pumps and boiler aren't running, check to see if damp.
Do you know how high above the pumps the header tank is? I doubt its cavitation but thought I'd ask.
Yes I would put a manual air vent near the cylinder and possibly remove the one near pumps.
Also out of curiosity do you know how that system is wired with two pumps? Do you only get heating when hot water is on or is the a relay somewhere?

Thanks again SJB
Air vent at boiler seems to be dry all the time so probably not leaking.
The header tank is in attic . ( two storey house) boiler in garage .
Nor sure exactly how it is wired but Horstman controller in kitchen allows for HW and Heating or Hot water only. In boiler house each pump and boiler have isolation switches.
I will try changing the orientation of the pumps as snowman suggested and fit a new automatic air vent .
Thanks and Happy Xmas!

 

[SJB060685]

Thanks for clarifying my suspicion on the wiring. Yes the header tank is high enough to avoid cavitation, I thought it would be but was just checking. Do as you said and report back to us please.
Merry Christmas my friend

 

[Beardyoldman]

Hi there SJB / Snowman
Reporting back .......First the good news! ....discovered what the problem was ......and yes the bad news is the boiler is leaking water and about to go .It is actually 16 years old so suppose I can’t complain to much.
On another note we would like to replace the oil boiler with gas Combi however there is a waiting time of approx 8 weeks. If and when the existing boiler goes it will leave the system without any water.....will this cause corrosion problems? If so as a temporary measure would it be wise to bypass boiler and refill system with inhibitor until the new installation is carried out?
Thanks

 

[SJB060685]

Hi there SJB / Snowman
Reporting back ...First the good news! ..discovered what the problem was ....and yes the bad news is the boiler is leaking water and about to go .It is actually 16 years old so suppose I can’t complain to much.
On another note we would like to replace the oil boiler with gas Combi however there is a waiting time of approx 8 weeks. If and when the existing boiler goes it will leave the system without any water...will this cause corrosion problems? If so as a temporary measure would it be wise to bypass boiler and refill system with inhibitor until the new installation is carried out?
Thanks

Glad you found the problem, sorry the verdict is a bad one. From what you've said when the boiler is running it's under a negative pressure and drawing the air in, when the pump stops the water will then leak.
I cant comment on the gas side of things as I'm not qualified.
If you're replacing the boiler then not only is it a good time but also required to power flush the system and make adjustments. There are products on the market, plus some old theoretical ideas to stem the leakage in the meantime.