Grundfos pump making unusual sound/boiler not coming on

[Stephen JW]

First post so greetings to all!

We have a problem with our elderly Potterton boiler and its Grundfos pump as follows:

• Boiler started behaving erratically, switching on & off at short intervals
• Within days boiler stopped coming on at all
• Noticed that Grundfos pump was making an unusual sound as though struggling to function
• Tried method shown here without success:

Am I correct in assuming that the boiler is not working due to loss of pressure because the pump is not circulating the water through the system?

• NOTE that when the programmer was replaced a couple of years ago with a Drayton Lp112 the person installing it wired it incorrectly so that the heating and hot water could not be controlled separately. It has been like it ever since.

We would appreciate advice as to how to best tackle this problem, bearing in mind the following:

• We are looking for a short term affordable solution as we will be moving house in the next 12-18 months
• We do not have the funds for a full system replacement at this time

Many thanks!

Stephen

 

[Deleted member 120897]

Greetings Stephen, I’m confused, has the boiler lost pressure and now not functioning, or is it the pump noise or both? Which potterton boiler? are you bothered for now about fixing the programmer?

 

[steadyon]

1. If the pump spindle is not turning when the pump is on, then it has a fault.
2. If water is not circulating fast enough, the boiler will overheat and turn itself off. Its not a pressure issue, more a flow one.
3. Not sure about your boiler, but some will detect whether pump is running or not, and if not will not turn on.
4. I suspect you are going to need a new pump. As you have a system boiler with the pump inside you are probably forced to buy one at Vaillant prices and pay to have it fitted by a Gas Safe registered person.
5. There is a possibility that a circuit board fault, or other boiler internal fault, is causing the pump not to start, but given that it was making unusual noises, this seems unlikely.
6. I think your first port of call should be a boiler repair person, preferably one with Vaillant experience. Some manufacturers do a "fixed price" fault repair service. Worth finding out if Vaillant do this if you can't find someone locally.

 

[Stephen JW]

Greetings Stephen, I’m confused, has the boiler lost pressure and now not functioning, or is it the pump noise or both? Which potterton boiler? are you bothered for now about fixing the programmer?

Hi there

Many thanks for the fast response! And thanks in advance for any advice you may be able to give me.

I'm confused too, which was the reason I posted my query here. The extent of my understanding of the problem(s) was listed in the bullet points of my first post.

The boiler is a Potterton Netaheat Profile of indeterminate age. It has no external pressure gauge so (as a lay person) I have no way of telling whether it has lost pressure. My question was as to whether the pump (Grindfos Selectric UPS 15-50) malfunctioning would cause loss of pressure that would prevent the boiler from coming on at all. Or to put it another way, whether I have one problem here or two separate problems that have coincided. Note that the pump body gets hot when the system is switched on but the pipework around it does not.

Its not essential to have the programmer correctly rewired at the present time, but if the overall solution to the immediate problem was the replacement of the pump only, it would be preferable if it could be done at the same time.

Many thanks again!

 

[Deleted member 120897]

Ok, so you have tanks in the loft then - not a pressure gauge. So a lack of water in the system, a sticking pump or faulty capacitor (but like a starter motor) could cause this issue. I suspect the pump isn’t circulating as you have kind of describe, so follow the video you posted and try and turn the pump/circulator shaft. If the pump sounds like it’s trying to kick in, but just a slight humming noise, then i suspect the capacitor. If the heating system worked recently, but has stopped I suspect the water in the system is fine.

 

[Stephen JW]

1. If the pump spindle is not turning when the pump is on, then it has a fault.
2. If water is not circulating fast enough, the boiler will overheat and turn itself off. Its not a pressure issue, more a flow one.
3. Not sure about your boiler, but some will detect whether pump is running or not, and if not will not turn on.
4. I suspect you are going to need a new pump. As you have a system boiler with the pump inside you are probably forced to buy one at Vaillant prices and pay to have it fitted by a Gas Safe registered person.
5. There is a possibility that a circuit board fault, or other boiler internal fault, is causing the pump not to start, but given that it was making unusual noises, this seems unlikely.
6. I think your first port of call should be a boiler repair person, preferably one with Vaillant experience. Some manufacturers do a "fixed price" fault repair service. Worth finding out if Vaillant do this if you can't find someone locally.

Thanks for your helpful reply. Just to clarify the boiler is a Potterton Netaheat Profile and the Grundfos Selectric UPS 15-50 pump is in the airing cupboard.

 

[Deleted member 120897]

1. If the pump spindle is not turning when the pump is on, then it has a fault.
2. If water is not circulating fast enough, the boiler will overheat and turn itself off. Its not a pressure issue, more a flow one.
3. Not sure about your boiler, but some will detect whether pump is running or not, and if not will not turn on.
4. I suspect you are going to need a new pump. As you have a system boiler with the pump inside you are probably forced to buy one at Vaillant prices and pay to have it fitted by a Gas Safe registered person.
5. There is a possibility that a circuit board fault, or other boiler internal fault, is causing the pump not to start, but given that it was making unusual noises, this seems unlikely.
6. I think your first port of call should be a boiler repair person, preferably one with Vaillant experience. Some manufacturers do a "fixed price" fault repair service. Worth finding out if Vaillant do this if you can't find someone locally.

OP has Potterton boiler, the video is just a link to YouTube, using a Vaillant pump, obviously causing the confusion.

 

[Stephen JW]

Ok, so you have tanks in the loft then - not a pressure gauge. So a lack of water in the system, a sticking pump or faulty capacitor (but like a starter motor) could cause this issue. I suspect the pump isn’t circulating as you have kind of describe, so follow the video you posted and try and turn the pump/circulator shaft. If the pump sounds like it’s trying to kick in, but just a slight humming noise, then i suspect the capacitor. If the heating system worked recently, but has stopped I suspect the water in the system is fine.

Ah that's great as you seem to have eliminated two out of three of those possibilities. I did try the method shown in the video and the pump impeller was turning freely. I have also checked the small tank in the loft and it is full. Which seems to leave just the capacitor. I should mention that the fault actually occurred a few weeks ago but we have been managing for hot water with the electric immersion heater. Would you anticipate having left the system idle for this length of time causing any additional problems? Many thanks again.

 

[Deleted member 120897]

Would you anticipate having left the system idle for this length of time causing any additional problems? Many thanks again

No I wouldn’t. When you spun the impeller, was there a demand on, eg heating or hot water?

 

[Stephen JW]

No I wouldn’t. When you spun the impeller, was there a demand on, eg heating or hot water?

Thanks again for all your replies. Apologies if I am misunderstanding your question but the boiler and programmer were both off when I spun the impeller with a screwdriver. I thought this was correct.

 

[ShaunCorbs]

No should be powered / running

 

[Stephen JW]

No should be powered / running

Thank you! I will try that again then.

 

[Deleted member 120897]

If it springs into life when you try it with power on, then new capacitor or pump required.

 

[Stephen JW]

If it springs into life when you try it with power on, then new capacitor or pump required.

Just tried that. When I removed the centre screw the impeller screw head was visibly turning but the pump was still making the same abnormal sound and the boiler is not igniting. The same sound can be heard in the boiler cupboard. Difficult to describe but it sounds as though water is trying to circulate around the system but certainly not running smoothly. The pump is old, would it be practical or indeed sensible to replace the capacitor only, or would it be wiser to replace the entire pump assembly with a new one? Many thanks

 

[exedon2]

Time to move on and change pump
Dab evosta 3 is our replacement pump of choice.
Better price than grundfos and Dab is owned by grundfos!

 

[ShaunCorbs]

Time to move on and change pump
Dab evosta 3 is our replacement pump of choice.
Better price than grundfos and Dab is owned by grundfos!

Can’t it’s inbuilt to the boiler and has to be original

 

[exedon2]

Op says in #6 pump is in airing cupboard

 

[ShaunCorbs]

Op says in #6 pump is in airing cupboard

Video shows the pump in the boiler

 

[Deleted member 120897]

Video shows the pump in the boiler

It’s a YouTube link showing a repair (general video), hence why steadyon mentioned Vaillant, boiler is potterton.

 

[Stephen JW]

It’s a YouTube link showing a repair (general video), hence why steadyon mentioned Vaillant, boiler is potterton.

Video shows the pump in the boiler

Apologies for the confusion I have unintentionally caused by posting the link to this YouTube video. I linked to this as a reference to something I had already tried to free the impeller. I hadn't realised that the link and video 'thumbnail' would appear as a huge image within the post!

 

[Stephen JW]

If it springs into life when you try it with power on, then new capacitor or pump required.

Belated thanks for all your help with this. Work has now been done. New Grundfos UPS3 15-50/65 pump fitted and controller now correctly wired so water and heating can be programmed independently. He also changed the 3-port valve as it transpired that the person that wired the replacement controller incorrectly also fitted the wrong type of valve for the system. Boiler and system is now running the most efficiently it has for years. However there is now a noticeable hum resonating through the system that builds up shortly after it switches on. Strangely it seems louder in the downstairs cloakroom than it does in the airing cupboard itself. If you hold the pipes adjacent to the pump there is a slight vibration that seems to correspond with the frequency of the hum. Any helpful suggestions gratefully received. Thanks!

 

[John.g]

The UPS 3 is a very powerful pump and if set very high can cause problems, can you take a photo of the settings, they will correspond to one of these settings.
It comes factory set to its max, constant curve iii

 

[Stephen JW]

The UPS 3 is a very powerful pump and if set very high can cause problems, can you take a photo of the settings, they will correspond to one of these settings.
It comes factory set to its max, constant curve iii

View attachment 65079

Thanks John

It does seem to be set to the factory default. I have attached a couple of photos, one of the non-working original pump and one of the new UPS 3. The orientation of the UPS 3 is as seen (i.e. the photo is the correct way up).

As I said previously the system is running really well apart from the resonating noise. What setting would you suggest? The boiler is an old Potterton Netaheat Profile (annually serviced).

Many thanks again

 

[John.g]

Hi Stephen,
Would suggest either PPII, which is nominally 3.8M but should run at around 2.5/2.6M at your demand OR CPI which runs at a constant 3M head.
CCIII meant you were more than likely running at a 6M head, no need, this is only used on pump installation and should be only run at this head for about 10 mins to assist in venting air.

You probably know how its done but press and hold the setting button for 3 secs to change pump modes, then briefly press to select the correct mode setting.

 

[Stephen JW]

Hi Stephen,
Would suggest either PPII, which is nominally 3.8M but should run at around 2.5/2.6M at your demand OR CPI which runs at a constant 3M head.
CCIII meant you were more than likely running at a 6M head, no need, this is only used on pump installation and should be only run at this head for about 10 mins to assist in venting air.

You probably know how its done but press and hold the setting button for 3 secs to change pump modes, then briefly press to select the correct mode setting.

View attachment 65107

Thanks John. We tried that. In PPI, PPII, CPI & CPII setting the LEDs remained flashing and the pump didn't start running. We put it back into Constant Curve mode and selected CCII mode. It seemed to be struggling on CCI. Are we missing something obvious here? Many thanks again for your time and helpful advice John.

 

[John.g]

ALL the PP & CP modes operate with flashing LEDs (see below) so if lighting in any of the modes below as shown then the pump will/should be running. (but very quietly)

What do you mean by struggling?.

If CCI is too weak at 4.2M then not a hope of enough circulation on PPII or CPI.
If happy with CCII at 5.2M then leave it or perhaps try CPII at 4.5M which may give quiet running with enough head.

 

[Stephen JW]

ALL the PP & CP modes operate with flashing LEDs (see below) so if lighting in any of the modes below as shown then the pump will/should be running. (but very quietly)

What do you mean by struggling?.

If CCI is too weak at 4.2M then not a hope of enough circulation on PPII or CPI.
If happy with CCII at 5.2M then leave it or perhaps try CPII at 4.5M which may give quiet running with enough head.

View attachment 65116

Thanks John. Ah OK didn't realise that the LEDs were supposed to flash. When I said struggling I just meant that the pump didn't start straight away, not sure what would have happened if I had given it time? On CCII one of the radiators didn't heat at all and another was lukewarm. Now the boiler has switched off and all the radiators are cooling down. No resonating noise at CCII but it's looking like the system only supplies all the radiators at CCIII which is somewhat concerning bearing in mind your previous remarks. Note that our system ran well for many years with our old Grundfos Selectric 15-50 pump until it failed recently. Would the type of 3-port valve fitted have any bearing on this? It's a Drayton. Apologies for my lack of knowledge regarding this stuff and thanks again for your advice. Stephen

 

[John.g]

What is the boiler power and is it a modulating boiler?

How many rads?.

IF the UPS3 is working properly then CCII is more powerful than CC3 was on your old 5M selectric.
The UPS3 on CCII will maintain +5M up to a demand of 1.1 m3/hr, 18.3LPM.
Also, there should be little or no delay in pump startup after changing settings.
Is the system clean as very dirty systems can build up magnetite on these pump rotors which can slow them down or stop them, the pump head can be removed for cleaning.

 

[ShaunCorbs]

What was the old pump like eg in the outlets of the pump any blockage or was it clean and around 15mm dia ?

 

[John.g]

Here is the Selectric 15-50 Pump curve which gives a head of 4.2M @ 1.1m3/hr (0.306 l/s) on CC3 vs the UPS3's 5M @ 1.1m3/hr 0n CC2 so something amiss.

 

[Stephen JW]

What was the old pump like eg in the outlets of the pump any blockage or was it clean and around 15mm dia ?

What was the old pump like eg in the outlets of the pump any blockage or was it clean and around 15mm dia ?

What is the boiler power and is it a modulating boiler?

How many rads?.

IF the UPS3 is working properly then CCII is more powerful than CC3 was on your old 5M selectric.
The UPS3 on CCII will maintain +5M up to a demand of 1.1 m3/hr, 18.3LPM.
Also, there should be little or no delay in pump startup after changing settings.
Is the system clean as very dirty systems can build up magnetite on these pump rotors which can slow them down or stop them, the pump head can be removed for cleaning.

Hi John. Thanks for all the information you have provided. This is a steep learning curve for me as I am a complete layman and unfamiliar with the terminology and power ratings etc. But this is what I do know:

Boiler is Potterton Netaheat 50e which Google tells me is max. 14.65kw output

We have 10 radiators in all, smallest 72cm, largest 180cm

4 radiators + heated towel rail upstairs

3 long + 2 short radiators downstairs

The engineer drained, refilled and added inhibitor and fitted new valves with the new pump and 3-port valve.

When we put the pump back into CCIII after everything switched off on CCII last night the pump was ‘throbbing’ and making a ‘thrum-thrum-thrum’ sound as it was running. We left it for a few minutes to see if it would return to normal. It didn’t so we turned it off. This morning there was a lot of gurgling and ‘ticking’ but it is now running on CCIII as before. All radiators are hot. The resonating noise is back.

Many thanks again.

Stephen

 

[John.g]

Looks definitely like a pump problem there IMO, there were a few "dud" UPS3s sold, I would inform your engineer as a new pump should be supplied without question, under warranty, except that your system was/is filthy.
You can yourself just ensure that the pump isol valves are fully open and just recheck that the pump is orientated correctly, ie, if on the boiler flow side, pumping away from the boiler and if on the boiler return, pumping into it.

 

[Stephen JW]

Looks definitely like a pump problem there IMO, there were a few "dud" UPS3s sold, I would inform your engineer as a new pump should be supplied without question, under warranty, except that your system was/is filthy.
You can yourself just ensure that the pump isol valves are fully open and just recheck that the pump is orientated correctly, ie, if on the boiler flow side, pumping away from the boiler and if on the boiler return, pumping into it.

Thanks John. Sadly I don't know how to check these things. The pump itself is physically mounted upside down, presumably as if it were the 'correct' way up the mains cable and its mounting would prevent the airing cupboard door from closing. I have attached a few photos. A couple of further things to mention that may or may not be relevant.

1. Our system has no wall-mounted thermostat. We have old Servowarm thermostatic radiator valves on each rad.
2. We usually run the boiler on setting 3-4 on the control dial (range 1-5/max).

Thanks again!

 

[John.g]

There is an arrow on the pump body, see if its pointing up or down, then follow the pipe (up or down) and see where its attached to the diverter valve and we can soon figure it out.

The pump valves, just turn each one clockwise until shut then anticlockwise until fully open, it should take ~ 3 to 5 full turns each way to fully close/open them.

 

[John.g]

Didn't notice attachments before.......if the arrow on the pump body is pointing downwards then the pump is installed correctly.

 

[Stephen JW]

Didn't notice attachments before.......if the arrow on the pump body is pointing downwards then the pump is installed correctly.

Thanks John. Valves seem to be fully open. Can't see an arrow on the pump body. Where should I be looking?
Does the setting on our boiler that I mentioned have any bearing (3-4 on range 1-5/max) on things?. Likewise the thermostatic radiator valves?

 

[John.g]

Settings on boiler and TRVs are fine.

The pump arrow is on the pump body directly behind o the plug socket and is pointing upwards, probably downwards in your installation (on right hand side).


Can you also get a close up photo of the arrowed area in attachment.

And also around the pipework runs from the mid position valve to the cylinder coil flow and return etc.

 

[Stephen JW]

Settings on boiler and TRVs are fine.

The pump arrow is on the pump body directly behind o the plug socket and is pointing upwards, probably downwards in your installation (on right hand side).


Can you also get a close up photo of the arrowed area in attachment.

And also around the pipework runs from the mid position valve to the cylinder coil flow and return etc.

View attachment 65156

Arrow on pump was quite difficult to access and take snap of but have attached the best I could get. It is pointing down.

Also attached close up arrowed.

Many thanks

 

[John.g]

So pump is correct, the arrowed item is a mini ball valve by pass which is partially opened, can't see any reason why CCII shouldn't give perfectly acceptable flow rates compared to CCIII, it should give ~ 90%. so still points to pump problems IMO.
Its a bit surprising that your engineer didn't try out any other modes as most would settle traditionally for CCII even if they knew nothing about the other modes.

Also point out to him that the UPS3 CCII is more powerful than the Selectric CCIII.

Did your engineer make any other changes apart from the new pump & mid position valve?.

So, Stephen, If it were my installation, I would contact him and inform him of results, can't offer any other words of wisdom I'm afraid.

 

[Stephen JW]

So pump is correct, the arrowed item is a mini ball valve by pass which is partially opened, can't see any reason why CCII shouldn't give perfectly acceptable flow rates compared to CCIII, it should give ~ 90%. so still points to pump problems IMO.
Its a bit surprising that your engineer didn't try out any other modes as most would settle traditionally for CCII even if they knew nothing about the other modes.

Also point out to him that the UPS3 CCII is more powerful than the Selectric CCIII.

Did your engineer make any other changes apart from the new pump & mid position valve?.

So, Stephen, If it were my installation, I would contact him and inform him of results, can't offer any other words of wisdom I'm afraid.

Hi John. Firstly thank you so much for all your words of wisdom. You really have gone above and beyond to help and it is very much appreciated. It makes a huge difference to us to be able to call the engineer back knowing what it is reasonable to expect from the UPS3 in general and particularly, as you say, that UPS3 CCII is more powerful than our old pump - which supplied the system perfectly well for many years.

We are not aware of any other changes he made apart from fitting the Grundfos pump (and new pump valves), Drayton mid position valve and rewiring the (previously incorrectly wired) existing Drayton controller. He also drained and refilled the system.

Can I just ask couple more things before signing off?

The engineer initially quoted for a Honeywell mid position valve but actually supplied a Drayton. We didn't query this as the controller is a Drayton. Is this likely to have any bearing on the issue?

I only noticed after our last exchange of messages that, after I tried different pump settings and returned it to CCIII, one radiator that had previously been hot was lukewarm and one had not come on at all (both downstairs). I turned the boiler controller to 5 and both radiators came on. Any implications there?

And finally a (probably) really stupid question... should the circulating pump be constantly running when only hot water is selected on the controller?

Once again, many thanks for all your help John, you have been brilliant!

 

[John.g]

Mid position valve make should make no difference.

Don't think changing the boiler flow temperature should have any effect on the pump operation.

Pump should be constantly running with HW only selected as long as the cylinder stat is requesting heat.

Let us know how you get on.

 

[Stephen JW]

Mid position valve make should make no difference.

Don't think changing the boiler flow temperature should have any effect on the pump operation.

Pump should be constantly running with HW only selected as long as the cylinder stat is requesting heat.

Let us know how you get on.

Thanks so much John. Will do.

 

[Stephen JW]

Mid position valve make should make no difference.

Don't think changing the boiler flow temperature should have any effect on the pump operation.

Pump should be constantly running with HW only selected as long as the cylinder stat is requesting heat.

Let us know how you get on.

Good morning John

Not the response I imagine either of us expected me to post I’m afraid…

Apologies for the length of this post but as succinctly as possible…

• Engineer returned and suggested that running the pump on CCIII continuously was fine
• We said CCIII was noisy & resonating and that CCII was more powerful than our old pump
• Engineer said he would balance the radiators (but only adjusted 4-5 rads)
• Ran quietly on CCII for a couple of hours after he left but 2 upstairs radiators soon cooled
• Following morning successfully ran on CCII for an hour on water only – water very hot in < 1 hour
• Switched to heat (CCII) - only 3 upstairs rads fully hot, 5 downstairs warm only and 2 upstairs cold
• Within an hour boiler was mostly off and all rads cooling

We are waiting for the engineer to return but in the meantime we have tried various combos of heat only/water only/heat+water in both CCIII and CCII and have concluded the following:

• Since engineer ‘balanced’ the radiators 2 upstairs rads do not heat (1 cold/1 lukewarm) even in CCIII
• Pump and system is still noisy on CCIII (vibration can be felt through feet on floor outside airing cupboard)
• On CCIII in heat only mode the 8 radiators that do work get very hot
• Boiler continues to repeatedly fire up after the 8 working radiators have reached full heat
• On CCIII in water only mode water in the tank is fully hot (from cold) within 30mins
• On CCIII in heat+water mode 2 downstairs rads failed to reach full heat & water took 60mins to get hot
• Running heat+water seems to result in air getting into the system and the pump pulsing
• On CCII in water only mode system successfully fully heated the tank in < 1 hour
• On CCII in heat only mode system will run for an hour or so but ONLY AFTER rads have fully heated on CCIII first then switched to CCII
• Running on CCII after system had cooled for an hour (after running heat+water on CCIII) the downstairs rads failed to reach full heat after 90mins, pump started pulsing and the rads started to cool
• 2nd attempt to run heat only on CCII after the system had fully cooled resulted in pulsing after only 20-25 mins see attached video
• Switching on heat in CCII mode the morning after the above resulted in spluttering from the pump and the sound of rushing water see attached video

Summary:

We can run in CCIII in either heat only or water only but if we try to run heat+water together in CCIII or run other than water only in CCII we get problems that seem to be related to air getting into the system.

Could this be caused by a problem with the mid-position valve?

 

[John.g]

Its most likely that the air is a result in running in CCIII which is 6.4M, CCII should definitely be more than enough but obviously isn't. If we assume that the pump isn't faulty then I would shut that by pass fully, (see closeup.jpg post 38) put a mark opposite the slot ends and then either use a screwdriver or a allen key to turn the slot fully horizontallly and see if pump still noisy, even if it is retry it on CCII.

If you have 2 cold water storage tanks in your attic, check that the smaller of the two has water in it, you didn't say I think that you had this small tank but did say you didn't have a pressure gauge.

 

[Stephen JW]

Its most likely that the air is a result in running in CCIII which is 6.4M, CCII should definitely be more than enough but obviously isn't. If we assume that the pump isn't faulty then I would shut that by pass fully, (see closeup.jpg post 38) put a mark opposite the slot ends and then either use a screwdriver or a allen key to turn the slot fully horizontallly and see if pump still noisy, even if it is retry it on CCII.

If you have 2 cold water storage tanks in your attic, check that the smaller of the two has water in it, you didn't say I think that you had this small tank but did say you didn't have a pressure gauge.

Thanks John

Yes small tank is full & we don't have a pressure gauge. Just to be 100% sure I am adjusting the correct thing - we are talking about the attached valve, correct?

Interesting that you say that the air is a result of running in CCIII. I spoke to someone from Grundfos who told me to run it in CCIII to vent the air after it started pulsing in CCII.

Do you think that the pulsing and spluttering in the previously attached videos is indeed air in the system? Could the pump actually be faulty?

Thank you so much again!

 

[John.g]

That's the valve alright.

Running that pump in CCIII in a OV system will IMO lead to air ingress, its OK in a sealed system.

Are you getting any air from any of the rads etc?, also look into the small tank and see if any signs of agitation etc, while you are watching get somebody to start/stop the boiler and see if any water coming from the vent., also feel the cold water outlet from the tank and see if its hot. Is the tank clean?.
Can't really say if the pump is faulty or not, there may be a blockage somewhere in the cold feed, can you see where it joins the system?., if the system was drained down recently and refilled then unlikely that its blocked.

 

[Stephen JW]

That's the valve alright.

Running that pump in CCIII in a OV system will IMO lead to air ingress, its OK in a sealed system.

Are you getting any air from any of the rads etc?, also look into the small tank and see if any signs of agitation etc, while you are watching get somebody to start/stop the boiler and see if any water coming from the vent., also feel the cold water outlet from the tank and see if its hot. Is the tank clean?.
Can't really say if the pump is faulty or not, there may be a blockage somewhere in the cold feed, can you see where it joins the system?., if the system was drained down recently and refilled then unlikely that its blocked.

Many thanks again. The engineer turned up unexpectedly this afternoon and decided to change the pump. Will report back as soon as we have had a change to run it thoroughly.

Hadn't yet tried the by pass. Mentioned it to the engineer but he said it was seized up in that position. Fingers crossed!

 

[fronty]

Reading this with interest I was thinking that the radiators might need balancing, if some rads don't get hot on CCII then then their lockshield valves might need opening. It sounds like your man started this but didn't finish, it can take several days to complete, there is a sticky thread at the top of the forum, I would give that a go.

 

[fronty]

FYI I have a grundfos pump, a but different to yours but it has various modes including some constant speed modes I, II & III, I run mine on speed II as like you found that III was too noisy. I have 14 radiators and this setting works perfectly for me.

 

[John.g]

Agree, I have 10 rads (no balancing), OV system, on a 4.4M PP setting (Wilo Yonos Pico) which gives ~ 14LPM @ 3.2M.
The UPS3 flows 18.3LPM @ 6.3M on CCIII & 18.3LPM @ 5.0M on CCII.

As a matter of interest what model Grundfos do you have?.