Over Pumping After Pump Replacement

tb66

Changed pump on oil central heating yesterday. Its an open system heating rads only. Pump in external boiler house next to boiler on return pipe. Fully drained system down to replace as old pump valves need to be cut off and flushed it out while had chance. Put new pump in and fired up and all good till I noticed it was over pumping on every pump setting. There is a penny valve on expansion tank outlet so I disconnected boiler, ran pump on its own(with expansion off) and all is good but as soon as expansion tank is back in play it over pumps.

The old pump was 5mtr head this one is 6mtr but just a basic cheap 3 speed pump. I have obviously fully bled all rads and pump and after flushing system the water was nearly clear so airlock or blockage is unlikely.

I have pump flow direction towards boiler as previous one was. Was considering should I move pump to flow pipe but not sure if that likely to give same result.

Anyone and idea? I just hoping I missing something obvious here.

DublinDilbert

Is it over pumping if you run the pump with the boiler off?

Are there lots of trvs? Are they fully opened ?

tb66

https://www.boards.ie/discussion/comment/121033100#Comment_121033100

Yes, And all trvs and valves fully opened

John.G

What is the make/model of the old pump and what speed was it running on?, ditto re new pump.

Is the pump pumping into the boiler return

You may now have deposited sludge in the system after drain down.

What is the cold feed/vent arrangement, may be partial blockage here, now.

tb66

https://www.boards.ie/discussion/comment/121033196#Comment_121033196

Old pump was a Grundfoss about 10yrs old, I binned it. New one a Trident wrs25/60-130. From what I remember all was similar to other except its a 6mtr head

Pump is on return and towards boiler

Doubt the sludge, main system about 25yrs old but all rads changed and most pipework changed in last 3 yrs. Boiler original and old.

Cold feed/vent are original .Cant see layout as they boxed in but I had to undo/replace flow/return to boiler to remove pump and no sign of sludge there.I drained and cleaned system every year for last ages, just pump fittings were weeping and decided to change it and now this is happening.

Is it possible the pump is just too powerfull, altho its just a basic cheap 3 speed one from Amazon!!

Also it works fine with header tank blocked off but as soon as that is part of system the problem starts

John.G

A small book could be written on pump over problems on changing circ pumps, some systems are very very sensetive to the pump head depending on the vent/cold feed arrangement.

Your old pump may have been a Grundfoss Selectric, some of these had relatively low pump heads down to 2.0m on speed 1. Your new pump on speed1 at 3M shouldn't cause any problems but bearring in mind, the above, it may. Mode: 3 adjustable mode(power:100/70/55W,flow:45/35/28L/min,head:6/5/3M) (your new pump). You could just throttle in the pump discharge until no pump over but not really a cure long term.

I have a 50 year old oil fired OV system, some rads over 40 years old, with a (Wilo Yonos Pico) pump setting 0f 3.6M for 10 rads but even I was to run this at its full head of 6M with just one rad in service I wouldn't get pump over because pump over can't occur with my system, installed from new. I think you should establish what type of system you've got.

I am pumping into the boiler return as well.

Combined Cold Feed & Vent. rev1.JPG

tb66

https://www.boards.ie/discussion/comment/121033421#Comment_121033421

Was contemplating closing pump gate valves a bit but i guess that will mean a longer heat up time for rads and obviously not the proper fix. I can see the feed/return pipes enter the house where cylinder press is but disappear into ceiling so cant see what is between ceiling and attic as there fully boxed in in bedroom .At a guess Id suggest the feed/vent are just teed off the flow somewhere between attic and top of cylinder press. Major surgery would be needed to see that part of system and hoping to avoid that.

As it was working ok before with old pump regardless of low/high speed maybe I should try a plumbers merchant to see if they and old pumps lying about. Defo be an easier option than ripping out a section of wall that will need replastered etc.

John.G

How many rads?, you could, if prepared to spend around €100/€120 buy a Wilo Yonos Pico like mine which will give you any head you require settable in 0.1M increments or a cheaper smart pump, will get the name in a minute which should do the job as well.

In the meantime run the pump with the burner off and just throttle the pump discharge valve only, start with it shut , to see how far its opened to stop the pump over.

The other cheaper pump ~ €90 is a 6M Tucson but the fixed curves are 1M, 3M & 6m, so cant' recommend it as 1M is too low and your own pump has a 3M setting.

tb66

Ill chance throttling valve tomorrow but a variable head option pump may be an idea. Obviously 3mtr is too much, may look into even raising vent pipe in attic. I think i could probable raise it 1/2mt or so. System has 8 rads.

John.G

8 rads, say total output of 12kw will require a flowrate of 14.3LPM, 0,86m3/hr to give a reasonable rad dT of 12C so a 3M pump will then be running at ~ 2.5/2.7M, again should not normally cause a problem but if, for whatever reason, you have to reduce the head to say 1.6M, then the circ rate will still be 11.2LPM,0.67m3/hr with a ~ still acceptable dT of 15.4C, anyway see how the throttling goes.

Lenar3556

If there is no solid fuel, converting it to a sealed system may be a good long term solution.

As John has indicated, changing pumps can give rise to circulation and pitching problems not experienced previously. Why isn’t always obvious. Modulating pumps can be particularly troublesome.

tb66

https://www.boards.ie/discussion/comment/121036272#Comment_121036272

Sealed system I guess is way to go but there is defo some 25-30yo Acorn fittings and pipework on this and not sure they be up to the pressure and most are boxed in or under bedroom floor. I played around with valves on pump today and at just under half throttled it stopped pitching. Fired up boiler and all good, rads warm,no pitching/over pumping. Not the ideal solution but its working.

Guess someday Im going to have to open that boxed in part and lift bedroom floor and sort out that old pipework properly.

John.G

A remote possibility but listen when you quickly change pump speeds and ensure to hear three different speeds with speed 1 the lowest, 3M.

A 6m Wilo Yonos Pico will certainly give you precise control in 0.1M steps, throttling is fine but if your system is zoned or has TRVs then pitching quite possibly might re occur.

tb66

I can definitely hear the speed change with switching. No zone valves and only one TRV. Was in plumbing merchants today getting some fittings to raise vent pipe and they have the Wilo pump for €135. I will run this for a bit over next week and see how it works and if pitching reoccurs a new pump it is.

Thanks for advice John.

John.G

If that penny valve was installed when you changed the pumps then I would replace it with a gate valve or a full bore ball valve, if in place before the change over then no need.

tb66

Not new, its been there for years. Just to pick your brains and from reading other threads and forums. Would I be better to convert to combined feed/vent set up like yours. I believe this is not the "preferred" setup but seems lots have done it without issue. I could easily reroute the vent pipe, cut the feed at header tank and tee into vent pipe. The one thing I not sure about is I would only be able to blank the (now old)feed pipe in the attic and not below. Could this be an issue as this pipe likely to contain air with no escape route.

Just a extra option I thinking of if the current setup pitches again or boiler cuts out early cause water not flowing around quickly enough.Yesterday was a quick 30/40min heating run and although all seemed ok I probably need to give it a few hrs like the way it will be running in a few weeks.

John.G

May not be required but my (short) feed and vent are the same diameter, After cutting the feed at the header tank I would fit a ball valve with a plug on its end, when refilling, leave the ball valve cracked open and as soon as water comes out just shut it and insert the plug, pipe is then full of water and can't see it causing any issues. I also have a isolating (service) valve on the F&E tank ballcock makeup, when refilling the system just crack that open to fill the system very slowly in case of any trapped air, filling it slowly will (IMO) allow air to pass up the same pipe as the cold water is trickling down through.

tb66

I have read trapped air can be issue so do you mean you have a gate/lever valve on mains going to ballcock in F+E and when refilling close this a bit so tank only fills slowly? Valve on old feed great idea.

John.G

Yes, and only open it a little when refilling system, I keep mine shut permanently after refilling and open it once/twice per year to check for any leakages, I have never seen a single drop of water required for top up between drain downs.

tb66

Great, I will give system a good proper run and see how it gets on. If it works happy days, if not its combine pipes or a Wilo variable head pump.

Thanks again John.

John.G

Any update on your problem?.

tb66

https://www.boards.ie/discussion/comment/121059329#Comment_121059329

Gave it a good run over weekend and seems ok but I had to up the temp on stat on boiler to stop it cutting out too soon. I guess flow from return is just not quick enough to cool it down sufficiently. Also realized combining flow/return is going to be a nightmare as the vent pipe enters attic above a purlin and is behind the main tank. I would need arms about 6ft long to cut and join to bring to attic floor level unless I remove the main tank for access. Raising the header tank to suit would mean making some kind of plinth and would have a very short vent. It would also block up a lot of attic space as it would have to be right in middle of attic floor.

I think I will bite the bullet a buy the Wilo pump. Hopefully by adjusting the head to suit system I should not have to throttle the water flow through boiler.

John.G

In post#7 you said "As it was working ok before with old pump regardless of low/high speed", you would think that the "high" speed on the old pump should be 5M so why problems now with the new pump at 3M and even less with throttling??, you only drained the system down. However, it is what it is and you won't go wrong in installing the 6M Wilo Yonos Pico, I think these newer models now display the flowrate as well which is handy.

What is the boiler (make) and output?. I have a 18 year old Firebird jetted to give ~ 20kw output, even though I have a OV system there is a 3bar PRV mounted on top of the boiler which I use to vent the air from the boiler after any drain down, if I don't the boiler would lock out on the hi limit stat.

tb66

With all this hassle I totally forgot I did swap out a double rad for large single rad during summer to prevent a new sofa protruding out too much. Maybe that altered system dynamics to cause this? Boiler is old Worcester. Id say about 30yrs but in good shape and still does the business.

Was in merchants earlier and pump not in stock but will have by end of week. Pic of boiler spec attached.

John.G

I don't think the single panel rad should mke any difference except its a column type which may trap air in the top but something seems to have changed, do you feel much temperature difference between the boiler flow & return?

tb66

When it up and running to temp, the flow is uncomfortable to hold for any length of time.The return is warm but nothing like flow.All upstairs rads very warm over all the panel, downstairs ones very warm on top but noticeable difference on bottom. I didnt balance them proper yet but I guess could sort that.

John.G

When/if you install the Wilo then you can check head and flow and go from there.

tb66

Thats the plan. All being well, should get new pump installed on Sat. Hopefully that sorts it 🙏