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Discuss Grundfos pump making unusual sound/boiler not coming on in the Central Heating Forum area at PlumbersForums.net

Messages
2,199
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.
 
Messages
23
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.
 
Messages
23
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?
 

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2,199
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.
 
Last edited:
Messages
23
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!
 

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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.
 
Messages
23
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!
 
Messages
105
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.
 
Messages
105
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.
 
Messages
2,199
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?.
 
Messages
23
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?.
Hi John

So it seems that you were correct when you deduced that it was most likely a faulty pump back in post #32! Just a pity that it took our guy so long to concur and change it.

He replaced the pump and rebalanced the upstairs rads 2 days ago. He left it running on CCIII.

The pump was near silent running in CCIII and there was no vibration or resonating in the system.

Yesterday we tried CCII and that works perfectly as well.

We have set the TRVs between 2 & 3 and the boiler to 3.5.

All radiators are hot (top to bottom, corner to corner) within 20 minutes.

Boiler is running smoothly and quietly. We can’t remember the system ever running as quietly as it is now.

Once again thank you so much for all your help with this. I have learnt so much from you, which was an invaluable help in arguing the case for it being a faulty pump.
 
Messages
2,199
That's great to hear.
You could also run it on CPII which gives 95% of CCII flowrate and will save a extra bit of energy when the TRV's start throttling in. Unfortunately, the PP settings which were primarily designed for TRV operation are practically useless on this pump as they are too low except that you have very large flow and return manifolds but I suppose no harm in trying, its only a button push. IMO the DAB Evosta3 is a far better choice ( Ithink, made or owned by Grundfos) as not only has it higher PP settings but also displays the pump head and flow rate.
 

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