Vaillant boiler taking ages to get to target temperature

[b21playa]

At 75C/55C you are getting 29.3kw rad output or 89.2% of your 33.5kw T50 rating, if you were to run at a flow temperature of 65C then you will get a return temperature of 49.4C with 22.81kw rad output or 68.1% of your 33.5kw T50 rating, so a 24kw boiler may be ok especially as you probably won't be running two zones together for very long periods.

Many thanks John, your help is much appreciated.

I’ll arrange for boiler to be replaced in the new year along with reinstating the LLH and taking advice from Timmy for addding a filter to the secondary return, a ntc sensor and setting pump speed to constant. Just need to work out how to wire it up and program the boiler

 

[John.g]

Let us know how you get on.

I was looking at those UPS3 PP2 curves the other day for someone else and unless I misunderstood, you said that (with LLH in service) with d.00 set to 20kw and both zones on that you were still getting the boiler target temp of 75C, we now know that the primary flowrate is ~ 22LPM so the secondary flowrate must only have been ~ 7LPM to reduce the rad output to ~20kw. I would be surprised if a secondary head of more than 3M would be required to give a (secondary) flowrate of 22LPM, the UPS3 on PP2 will almost produce that, (it will give 19.5LPM at 2.6M) so looks to me like the pump isn't working as it should (or else some fundamental LLH problem), it might be worth removing the pump head and cleaning out the pump ports and also the impeller vanes, a tie wrap is handy for this, if all clean then the pump may have developed a fault, unfortunately this and a lot of other Grundfoss pumps don't display the power in watts from which the performance can easily be derived from the pump curves, you can allways stick a energy monitor on the end of the pump cable. Anyhow, one way or the other, worth bearing in mind.

 

[b21playa]

Let us know how you get on.

I was looking at those UPS3 PP2 curves the other day for someone else and unless I misunderstood, you said that (with LLH in service) with d.00 set to 20kw and both zones on that you were still getting the boiler target temp of 75C, we now know that the primary flowrate is ~ 22LPM so the secondary flowrate must only have been ~ 7LPM to reduce the rad output to ~20kw. I would be surprised if a secondary head of more than 3M would be required to give a (secondary) flowrate of 22LPM, the UPS3 on PP2 will almost produce that, (it will give 19.5LPM at 2.6M) so looks to me like the pump isn't working as it should (or else some fundamental LLH problem), it might be worth removing the pump head and cleaning out the pump ports and also the impeller vanes, a tie wrap is handy for this, if all clean then the pump may have developed a fault, unfortunately this and a lot of other Grundfoss pumps don't display the power in watts from which the performance can easily be derived from the pump curves, you can allways stick a energy monitor on the end of the pump cable. Anyhow, one way or the other, worth bearing in mind.

I will keep you all posted - just waiting on a date from the rgi, I’m on the cancellation list if anytime comes up.

I’ll take a look at the pump tomorrow and see if it’s blocked and not spinning freely. I wonder if it was the pipework, the flow comes out the pump and then has 2 x 90deg bends to go back on itself. There also wasn’t an air vent on the bend (highest point in that leg)

If the pump is bad, are there any better alternatives?

 

[John.g]

After inspection/cleaning you can then re try it with the re installed LLH, a few temperatures will then establish if its OK or not.
The 6M DAB Evosta3 is a good choice or my own (4 year old) 6M Wilo Yonos Pico with the 3 traditional CC settings plus CP and PP modes which can be incrementally changed in 0.1M steps to give almost any required flowrate. Both of these pumps display the power and the flowrate.

 

[b21playa]

After inspection/cleaning you can then re try it with the re installed LLH, a few temperatures will then establish if its OK or not.
The 6M DAB Evosta3 is a good choice or my own (4 year old) 6M Wilo Yonos Pico with the 3 traditional CC settings plus CP and PP modes which can be incrementally changed in 0.1M steps to give almost any required flowrate. Both of these pumps display the power and the flowrate.

I’ll test it all before buying a new one, could be dirty, could be due to the way it was piped originally. Easy enough to change at a later date anyway

 

[b21playa]

Re install LLH.

Move second filter from primary flow to secondary return in to LLH.

Set secondary pump to constant. You want LLH flow in/out to be the same to prevent return water mixing. Can roughly check with temp probes on all LLH connections.

Set boiler to auto, not limited.

Get a vaillant LLH sensor (ntc) and attach to LLH and boiler.

Set to 65c, ensure return is low enough to condensate.

Forget about it and spend your energy somewhere else 🙂.

Hi Timmy

Should I move the filter from the primary return to secondary return or get another one?

Thanks

 

[b21playa]

Let us know how you get on.

I was looking at those UPS3 PP2 curves the other day for someone else and unless I misunderstood, you said that (with LLH in service) with d.00 set to 20kw and both zones on that you were still getting the boiler target temp of 75C, we now know that the primary flowrate is ~ 22LPM so the secondary flowrate must only have been ~ 7LPM to reduce the rad output to ~20kw. I would be surprised if a secondary head of more than 3M would be required to give a (secondary) flowrate of 22LPM, the UPS3 on PP2 will almost produce that, (it will give 19.5LPM at 2.6M) so looks to me like the pump isn't working as it should (or else some fundamental LLH problem), it might be worth removing the pump head and cleaning out the pump ports and also the impeller vanes, a tie wrap is handy for this, if all clean then the pump may have developed a fault, unfortunately this and a lot of other Grundfoss pumps don't display the power in watts from which the performance can easily be derived from the pump curves, you can allways stick a energy monitor on the end of the pump cable. Anyhow, one way or the other, worth bearing in mind.

Took the head off the pump today; impeller turned fine but there seemed to be some ‘end float’ which I’m not sure if it’s normal

Water colour wasn’t the best so I’ve added some cleaner and connected my twin magnacleanse

 

[John.g]

Took the head off the pump today; impeller turned fine but there seemed to be some ‘end float’ which I’m not sure if it’s normal

Water colour wasn’t the best so I’ve added some cleaner and connected my twin magnacleanse

That looks like excessive wear on the housing where the impeller fits into??, the pump looks quite reasonably clean IMO.
If you have the time/inclination I would suggest to buy a plug in energy monitor like mine below (~ £15ish) and connect a 3 pin plug to the pump cable, connect a mains supply to the pump inlet (as long as its not > say 5bar) stick a bit of pipe on the pump discharge with a gate/lever isolating valve (or a old pump isolating valve with a bit of pipe on the end) on the end, run the pump from a extension lead at say CC1, CC2, CC3 and PP2, and measure the flowrate into a bucket with the valve throttled to give a suitable flowrate (can check that later) and note the power from the energy monitor.