Inadequate Circulator Pump?

[JC22024]

My house is a 1970s build fairly well insulted detached 2 storey. Split in 2no zones which are controlled independently with digital thermostats and rarely run at the same time.

Downstairs has 9 double rads and 5 single rads.

Upstairs has 5 double rads and 1 single rad.

Open vent system std heat only oil condensing boiler 26kw.

About 10 years ago I swapped in a Grundfos Alpha 2 smart circulator pump. At the time this was in part due to radiator noise after installing TRV valves throughout the property and it did cure the noise.

Unfortunately I did not pay great attention to the balancing of the system. And only now when a new condensing oil std boiler has replaced the old one am I properly balancing the system again.

The pump is set to max constant speed 3 and showing about 38wattts power consumption on the display. Trouble is it does not seem to have nearly enough oomph to drive the heating system!

I noticed that of I turn most rads nearly off but still warm to touch I can get them all to show heat. But when I start to set the first ones to approx 11c drop across the other rads quickly die again and the boiler outlet pipe sits piping hot, return cool to touch and heat not going anywhere.

I think either the grundfos is starting to fail or I simply need a larger spec circulator pump in order to drive the water sufficiently around the house. Boiler located at one end of the house. 6 bedrooms house. So it has quite a path to go around.

Any recommendations for a replacement pump? Probably larger 180mm wide 8m head std unit not a smart one for a large property?

 

[ShaunCorbs]

Grundfos upm3 25-70 should help

 

[JC22024]

Grundfos upm3 25-70 should help

Thanks for that I looked it up there. 6.5m head is slightly higher than the Alpha 2 but some other pumps at 180mm wide have much higher output:

Central Heating Hot Water XTRA Large Capacity Circulation Pump by Trident. | eBay

TRIDENT WRS25/80-180 Central Heating Hot Water Large Capacity Circulation Circulating Pump. PREMIUM WATER PUMP. Max flow: 130L/min. Mode: 3 adjustable mode(power:248/200/150W,flow:60/70/80L/min,head:8/6/5M).

www.ebay.co.uk

Eg the grundfoss upm3 has 3.5m3 per hour capacity.

7.3m3 per hour capacity for the Trident pump above at max speed. Which I could turn down as needed.

I like Grundfos brand but I may need a larger flow pump.

 

[John.g]

If the new boiler is also 26kw then there should be no change in rad outputs with existing pump. If the boiler is running at 26kw continuously then a flow rate of 2.0M3/hr @ a dT of 11C which even a 6M pump will circulate at a head of ~ 3.5M. You possibly have a failing pump, can you post a photo of your one as there are a few different models, one at 38W on full speed = circulation rate of 5LPM at a 6M head, highly unlikely.
IMO a 8M Grundfos or preferably a 8M DAB Evosta should be quite sufficient for your needs bearing in mind that you have a 26kw boiler.

 

[ShaunCorbs]

Thanks for that I looked it up there. 6.5m head is slightly higher than the Alpha 2 but some other pumps at 180mm wide have much higher output:

Central Heating Hot Water XTRA Large Capacity Circulation Pump by Trident. | eBay

TRIDENT WRS25/80-180 Central Heating Hot Water Large Capacity Circulation Circulating Pump. PREMIUM WATER PUMP. Max flow: 130L/min. Mode: 3 adjustable mode(power:248/200/150W,flow:60/70/80L/min,head:8/6/5M).

www.ebay.co.uk

Eg the grundfoss upm3 has 3.5m3 per hour capacity.

7.3m3 per hour capacity for the Trident pump above at max speed. Which I could turn down as needed.

I like Grundfos brand but I may need a larger flow pump.

Where did you find the m3/h as the listing says it replaces the 15-60

The upm3 is roughly double the flow as your existing one 15mm - 25mm opening and impella

The thing you have to be careful of is your open vent so with too big of a pump it will pump over

 

[Chuck]

Just a thought but... does your system have an automatic bypass valve that might be short-circuiting the circulation because it hasn't been properly adjusted with the new boiler in situ, perhaps? Symptoms can be superficially similar to a weak pump.

 

[JC22024]

Where did you find the m3/h as the listing says it replaces the 15-60

The upm3 is roughly double the flow as your existing one 15mm - 25mm opening and impella

The thing you have to be careful of is your open vent so with too big of a pump it will pump over

Fair point on open vent - I found the specs on screwfix direct website. Grundfos are not very good at supplying figures in the data sheets! I will take a better search later today on specs of the upm3 it does sound good.

This is the old pump

 

[JC22024]

Just a thought but... does your system have an automatic bypass valve that might be short-circuiting the circulation because it hasn't been properly adjusted with the new boiler in situ, perhaps? Symptoms can be superficially similar to a weak pump.

Thanks- there is no mixing or bypass valve. The house has open vent system. In boiler room there are 28mm pipes which serve ground floor. Teed off of that is 22mm pipes for first floor. Motorised zone valves provide the control.

The house used to be one zone no stats. I updated it years ago to 2no zones for more control and efficiency. The TRV valves were also added and at some stage noises were heard from valves with old pump. A smart pump was solution or so I thought may have to consider a bypass valve if new pump doesn't play well.

 

[JC22024]

Boiler room is being tidied up, painted and pipes insulated now. But here is older photo showing install generally-

Return goes into bottom right of boiler. Flow out at top left. Vent is coming in at top right. Negative pump pressure at it with pump on outlet side of boiler. So no overflow issues at present. (Used to be years ago until pump was moved)

 

[ShaunCorbs]

Fair point on open vent - I found the specs on screwfix direct website. Grundfos are not very good at supplying figures in the data sheets! I will take a better search later today on specs of the upm3 it does sound good.

This is the old pump

View attachment 67134

Screwfix don’t stock Trident pumps ? Also they don’t stock upm3

 

[John.g]

Here are are the pump curves for a UPS 3. which IMO are quite adequate for your system with that 26kw boiler. On speed 3 it will circulate 2.0M3/hr @ a 4.3M head to satisfy a power rating of 26kw at a dT of 11C.
The Alpha 2 will only circulate 2M3/hr @ a 3.2M head. The pump in the photo is only showing 13W?.

 

[JC22024]

Here are are the pump curves for a UPS 3. which IMO are quite adequate for your system with that 26kw boiler. On speed 3 it will circulate 2.0M3/hr @ a 4.3M head to satisfy a power rating of 26kw at a dT of 11C.
The Alpha 2 will only circulate 2M3/hr @ a 3.2M head. The pump in the photo is only showing 13W?.

View attachment 67141

View attachment 67140

Yes I was trying different settings there but no difference. It has been on speed 3 ever since at 40w ish consumption. But can't appear to get beyond 2no first rads even on first floor circuit only! (When 11 degree drop is set on lockshields of first 2. Remaining rads full open and still dead)

Thanks for the curves - I believe it is a upm3 25-70 that was suggested? The pump has to travel quite a route from boiler room that's where I'm coming from VS boiler output. Which is downsize from old 26-32kw boiler due to more efficiency when using one zone or the other. (Since now the house is in 2no zones and I operate them independently)

 

[JC22024]

The head in my house is 6m. (Heating tank at top of loft)

So Grundfos - old @ 0.6m3/hr

Ups3 25-70 @ 0.8m3/hr

Doesn't appear like huge upgrade if my current pump isn't faulty but is undersize

EDIT - I may be reading the new pump chart incorrectly. It shows 5no curves so those must represent speed settings. In which case it could pump up to 1.5m3/hr

 

[John.g]

The elevation (height) of tank at 6M (or even 10M) doesn't mean that you need a 6M pump to overcome that head as its a closed system, if the flow&return piping are well sized then it may only require a pump (differential) head of 3M to overcome the pipe friction + other losses. Realistically, I would think you require a pump that will give a head of 4M at whatever flow rate you require. My 26kw Firebird boiler came with a nozzle sized to give 20kw output and yours may be likewise.

Which "new pump chart" are you referring to?, if its the Trident can you post the link to it?.

 

[JC22024]

The elevation (height) of tank at 6M (or even 10M) doesn't mean that you need a 6M pump to overcome that head as its a closed system, if the flow&return piping are well sized then it may only require a pump (differential) head of 3M to overcome the pipe friction + other losses. Realistically, I would think you require a pump that will give a head of 4M at whatever flow rate you require. My 26kw Firebird boiler came with a nozzle sized to give 20kw output and yours may be likewise.

Which "new pump chart" are you referring to?, if its the Trident can you post the link to it?

OK I presumed that as it is open vent system atmospheric pressure would have meant it was operating at lowest point of 6m head of water.

I don't have a curve for the Trident pump.

I was looking at a Grundfoss PDF which gave just one curve chart. And mentioned specific charts available per pump. Found a chart which may be pump specific in the link below:

Grundfos UPM3 Auto L 25-70 130mm Underfloor Heating Pump 240v

Buy Grundfos UPM3 Auto L 25-70 130mm Underfloor Heating Pump 240v Online at Anchor Pumps, Find the Best Price Anywhere Online, With Free Delivery.

www.anchorpumps.com

Swipe to the 2nd image for pump chart. It does appear to read more powerful than the older pump and I'll probably go for this Grunfos one as recommended

 

[ShaunCorbs]

Upm3 at 3.5 on speed two gives you approx 1.8m3h speed 3 2.5m3h

 

[John.g]

I suppose still slight chance that the pump is ok but blockage in main flow or return, as the pump is running at 38/40W then hard to see actual head/flow so suggest just c/o to CP1 & CP2 for a minute or two each and note the power, that might give a better idea of pump condition.

 

[JC22024]

I suppose still slight chance that the pump is ok but blockage in main flow or return, as the pump is running at 38/40W then hard to see actual head/flow so suggest just c/o to CP1 & CP2 for a minute or two each and note the power, that might give a better idea of pump condition.

OK after running on larger downstairs zone for 45 mins or so on speed setting III is was reading 33w.

On CP1 5w
CP2 7w after a few mins.




I remembered I had set the old circulator pump on garage shelf as a spare incase it failed. So I pulled it out there and slapped it in to see if it makes any difference to this as you say could also be a blockage.



The water I drained out of the system was light brown / clear. Not black. I had a Sentinel cleaing agent in it there for a week or so and drained down completely + re filled at weekend with new ball cock installed in header tank also. (Trying just to maintain the whole system)

Again the water I drained after the flush I did monitor and it was clear / light brown. So hopefully not a blockage per say but need to be mindful of that too thanks.

 

[John.g]

That old Wilo should certainly provide enough head for one zone on top speed.
There seems to be something wrong with the Alpha as the minimum power on CP1 is 13W and on CP2 is 22W, the minimum outputs on PP1 & PP2 are ~ 4.5W and 6W, more or less what you got.

Also (if I am looking at the right pump curves) the power output on speed3 when pumping 0 LPM is 33W!!.
If the Wilo is looking promising you might take the head off the Alpha and inspect/clean the vanes of the pump impeller and the pump ports, you might be able to clean the pump rotor at the same time.

 

[ShaunCorbs]

Jon it’s a 20 rad system

 

[John.g]

Yes, but those readings are all indicative of practically no circulation, if the pump discharge valve was closed fully, the readings would/should be the same, if I shut the discharge valve on my Wilo smart pump, the power readings will be exactly as its pump curves show for each different mode&setting at zero flow rates.

 

[ShaunCorbs]

Not really 33w on 3 on a pump 10 ish years old is moving / circulating and op says the system is working but the furthest away rads don’t fully heat / trouble balancing

 

[John.g]

Hard to disagree with that as 33W does seem very high for zero flow. Mine is 24W at zero flow, just tested it there now by shutting its discharge valve and its exactly as shown on its pump curve.
If the Alpha is re installed then quite simple to check it out by just shutting the discharge valve fully for 5/10 secs.

 

[JC22024]

Not really 33w on 3 on a pump 10 ish years old is moving / circulating and op says the system is working but the furthest away rads don’t fully heat / trouble balancing

OK so no change with the Wilo pump.

To explain this fully:

I have lived here since a child. Now 35. House has always been cold but I've done major upgrades to Building fabric in recent decade.

Heating always worked largely OK but also some rads were off always and never checked out. Pipes are 28mm on GF, 22mm on FF and 15mm to all rads no less than that.

House was renovated & extended over the years a couple of times in 80s.

Boiler is on one side of house so it has a job getting around all rads and back to boiler.

If I balance rads by feel only I get them all working on GF largest zone except furtherest away. If I turn others off then the furtherest one will come on hot.

Problem is even when the first floor small zone is on, when I balance first 2 rads accurately with thermometer to 11 degree drop, they feel toasty but then the other rads drop dead.

I do still believe the house simply requires a larger output circulator. This problem has existed for years and the new boiler is cranking out the heat but getting nowhere. I think for these purposes the Trident 180mm pump is worth a trial at least. If it proves the theory and I can balance rads properly and not lose heat / flow then can invest in a higher quality pump for long term use. Probably talking light commercial circulator here which I think the Trident may be albeit a cheap one.

 

[JC22024]

Sorry for poor quality but here is ground floor plan as example. Boiler is on far right wall.

It is back left bedroom that won't get hot when rads are balanced by feel only. Furtherest from boiler room

 

[JC22024]

OK better plan attached. (A bedroom single rad is removed at present)

Colour coded locations of rads on this Ground Floor. First floor is smaller on plan as it is a 1.5 storey house.

 

[ShaunCorbs]

Tbh my rule of thumb (engineers) 14-30 rads 25-80 under 15-60

 

[JC22024]

Tbh my rule of thumb (engineers) 14-30 rads 25-80 under 15-60

Thanks for that, am I right in thinking those figures may relate to

25mm inlet
80mm pump vane?

If so yes that would make sense as old units are 15mm inlet and 60mm vanes

 

[John.g]

GF only.
Does the boiler start to cycle a few minutes after a cold startup in the morning or does it run continuously for say 25/35 minutes before cycling?.

You have 28mm on the GF so a flowrate of 20LPM assuming 50M of pipework will require ~ 1M pump head, add another 1M for loss across rads etc then total head required = 2M so assuming no sludge in the system it should be no big deal to get sufficient circulation at least on the ground floor.
U/stairs with 22mm piping will require 3.4M to overcome pipe losses at 20LPM and 50M of piping, add another 1m across rads and total head required is 4.4M so a bigger problem for upstairs circulation.

 

[JC22024]

On cold start it will run for 15 or 20 mins then start cycling. Pipes in boiler room are roasting hot and return pipe always only max 25c at any time. (Usually return is stone cold)

I timed the cycling and of course this will vary with temps etc but it will stay off for 2.5 minutes and run again for 1.5mins. Does this constant. Pipes hardly touchable in boiler room so hot. Which makes me think the pump isn't drawing the water quickly enough around the circuit.

As I say I can get all rads to warm up bar one but not cranking enough room heat or near 11c drop.

 

[JC22024]

Good bad or indifferent I just bought a Trident 25/80 180 pump. Cheap enough to test anyway. If I'm wrong then so be it can set on garage shelf! Will be a pain to drain system again to open up pump from 130 to 180 but space to do it.

Really grateful for the great advice on here keep it coming! And of course I will let you all know in any event what difference if any the new pump makes and if it then allows me to balance rads properly without losing circulation.

Just want to keep after it now and get the heating system fully up to snuff if I can.

 

[John.g]

Something very strange going on, assuming boiler flow temp set to 70C then when the burner cuts out with a return temp of 25C means that you are only circulating 6LPM (0.36M3/hr) which equates to the 38W pump output you mentioned previously.
A running time of 37.5% is a average output of 7.5kw with a 20kw boiler or 9.75kw with a 26kw.
Can/have you checked that the circ pump stays running when the burner cuts out.

 

[JC22024]

Something very strange going on, assuming boiler flow temp set to 70C then when the burner cuts out with a return temp of 25C means that you are only circulating 6LPM (0.36M3/hr) which equates to the 38W pump output you mentioned previously.
A running time of 37.5% is a average output of 7.5kw with a 20kw boiler or 9.75kw with a 26kw.
Can/have you checked that the circ pump stays running when the burner cuts out.

Yes pump definitely stats powered up and all heating controls / valves are functioning correctly too

 

[JC22024]

I will check water quality when I drain it again and if dirty at all then I'll get more cleaner and run again with new larger pump. But water now coming out of rad vents is practically clear.

I do flush it out every few years too. I recall first time I did it when I was about 18 the water was pitch black and some rads had to come off and be flushed out with hose. Again this was 15 - 20 years ago.

 

[JC22024]

Upstairs has been running on its own tonight for a couple hours. 2 double rads hot and bathroom tall single hot.

On time = 1.5 mins. Off time= 4 mins 45 secs.

Return temp 43c




Again on the small upstairs zone I can get all rads warm. But when I balance first 2 correctly the rest fall off cold even with valves fully open.

It's on the larger downstairs circuit that the return temp never rises above 25c even after hours of running.