Vaillant boiler taking ages to get to target temperature

[John.g]

Thats interesting because (assuming a room(s) temp at 20C) that your rads are effectively "T36" which emit 65.2% of a T50 so, your rads output, 35.5*65.2%, 22.1kw which is probably why the LLH gave similar outputs with a boiler target temp of 75C but secondary temp of ~ 65C and your d0 setting of 20kw was sufficient to allow the boiler to reach its target temp of 75C.

If you didn't have that LLH to hand one wonders was one required in the first place?.

 

[b21playa]

Thats interesting because (assuming a room(s) temp at 20C) that your rads are effectively "T36" which emit 65.2% of a T50 so, your rads output, 35.5*65.2%, 22.1kw which is probably why the LLH gave similar outputs with a boiler target temp of 75C but secondary temp of ~ 65C and your d0 setting of 20kw was sufficient to allow the boiler to reach its target temp of 75C.

If you didn't have that LLH to hand one wonders was one required in the first place?.

Hi, thanks for that.

Just to clarify where has the 35.5 come from?

Thing one of the main reasons was the loss of head in the hex of the Vaillant and needing additional pump to circulate especially to loft rooms.

I may give it until Wednesday (my next free day) to put the LLH back in and see how the next few days go. Of course one zone at a time set at 20kw

 

[John.g]

That should read 33.5kw, "Just checked all rads, based on deltaT50 values upstairs circuit 14.8kw and downstairs 18.7kw" so your total rad output was ~ 21.8kw? (33.5*65.2%).
I obviously see your point re head loss.

 

[b21playa]

That should read 33.5kw, "Just checked all rads, based on deltaT50 values upstairs circuit 14.8kw and downstairs 18.7kw" so your total rad output was ~ 21.8kw? (33.5*65.2%).
I obviously see your point re head loss.

Thanks for clearing that up, makes sense and adds up.

Maybe that’s where the 24kw boiler made sense? I need to change the boiler at some point as something has dropped against it and damaged the casing

 

[John.g]

Well, all we know for sure is that the installed radiator output (T50) is 33.5kw, whether this is actually required at something like -10C or so is unknown except a heat loss was carried out, even if 24kw only is required and the rads are oversized, good, if weather compensation was installed which would give maximum boiler efficiency and even without it, you can manually set the boiler target temperature.

 

[b21playa]

Thanks for clearing that up, makes sense and adds up.

Well, all we know for sure is that the installed radiator output (T50) is 33.5kw, whether this is actually required at something like -10C or so is unknown except a heat loss was carried out, even if 24kw only is required and the rads are oversized, good, if weather compensation was installed which would give maximum boiler efficiency and even without it, you can manually set the boiler target temperature.

Rads are definitely oversized, the reason was to run a lower flow temp but that hasn’t happened yet….i have family members who really feel the cold (old age). No weather compensation fitted, just running hive units but have been thinking of upgrading controls but not sure which to go for. I’ve seen either Vaillant which seems expensive and can not work out exactly what I require or the other option was nest using open therm module

 

[John.g]

Did you ever actually measure the secondary flow temperature?, if the secondary pump which looks like a UPS3 is on PP2? setting then that can result in a very low actual head which may not have been sufficient for some rads.

 

[b21playa]

Did you ever actually measure the secondary flow temperature?, if the secondary pump which looks like a UPS3 is on PP2? setting then that can result in a very low actual head which may not have been sufficient for some rads.

I did at some point but can not remember the value unfortunately. Yes you are correct about the pump model and setting, I took that from the manual that it was recommended to be on PP2 but that was just for 2-pipe system. What would be the ideal setting from your experience?

 

[John.g]

I did at some point but can not remember the value unfortunately. Yes you are correct about the pump model and setting, I took that from the manual that it was recommended to be on PP2 but that was just for 2-pipe system. What would be the ideal setting wfrom your experience?

I've never even seen a LLH but think I have a fair idea of how they work, if you need the secondary flowtemp to be the same as the primary (boiler) flowtemp then the secondary flowrate has to equal to or less than the primary flowrate so a constant pressure or constant curve (speed) may be more appropriate but there's no point in overthinking it, the temperature gauge will give the best advise IMO.

 

[b21playa]

I've never even seen a LLH but think I have a fair idea of how they work, if you need the secondary flowtemp to be the same as the primary (boiler) flowtemp then the secondary flowrate has to equal to or less than the primary flowrate so a constant pressure or constant curve (speed) may be more appropriate but there's no point in overthinking it, the temperature gauge will give the best advise IMO.

Thanks John, much appreciated. Once I’ve fitted the LLH and get temp reading I’ll post back

 

[ShaunCorbs]

You do realise that extra 15 degrees is wasted energy/ warming the return up so not required

Does the boiler pump manage the load eg heats all of the rads etc ?

 

[b21playa]

You do realise that extra 15 degrees is wasted energy/ warming the return up so not required

Does the boiler pump manage the load eg heats all of the rads etc ?

Is 60degC the ideal flow temp?

I need to check all rads when just on boiler pump, I had checked earlier downstairs and a few in the 1st floor but not all of them and not the loft rads

 

[ShaunCorbs]

Well ideally your return needs to be below 50 for condensing boilers to be happy and with sensor mad vaillants this is a must also with your split as it won’t reach max burn / temps unless the split and temp rise is within spec (split is the difference between flow and return ideally 20dc)

 

[b21playa]

Well ideally your return needs to be below 50 for condensing boilers to be happy and with sensor mad vaillants this is a must also with your split as it won’t reach max burn / temps unless the split and temp rise is within spec (split is the difference between flow and return ideally 20dc)

Thanks. I’ve turned down flow to 65dC and will see how that goes.

Do you have any thoughts on replacing hive controls with one that can modulate the boiler better and set different flow temps for hw/ch?

 

[ShaunCorbs]

Thanks. I’ve turned down flow to 65dC and will see how that goes.

Do you have any thoughts on replacing hive controls with one that can modulate the boiler better and set different flow temps for hw/ch?

There brilliant and priority hot water and wc heating but you will have cooler rads then stock temp etc

 

[b21playa]

There brilliant and priority hot water and wc heating but you will have cooler rads then stock temp etc

Thanks. Vaillant controls are a bit of a mine field, not sure exactly what I would need? Vr66 wiring centre, weather comp sensor, not sure of which thermostats for both floors and then how to incorporate a vr10 sensor for dhw temp.

Hw priority would be great, can set flow at higher temp for quicker recharge

 

[John.g]

Thanks. Vaillant controls are a bit of a mine field, not sure exactly what I would need? Vr66 wiring centre, weather comp sensor, not sure of which thermostats for both floors and then how to incorporate a vr10 sensor for dhw temp.

Hw priority would be great, can set flow at higher temp for quicker recharge

Are you thinking of not re installing the LLH?.
How are the rads performing now at 65C??, if the return is like the previous 47C then you will be getting reasonable condensing and you may be able to further reduce the target temp. Are you still just running one zone at the time with d.00 set to 20kw or both with d.00 set to 30kw or whatever?.

 

[b21playa]

Are you thinking of not re installing the LLH?.
How are the rads performing now at 65C??, if the return is like the previous 47C then you will be getting reasonable condensing and you may be able to further reduce the target temp. Are you still just running one zone at the time with d.00 set to 20kw or both with d.00 set to 30kw or whatever?.

I’m thinking of leaving it for a bit as it is and see how it goes. Rads seem to be performing fine at 65c, don’t want to reduce anymore as cylinder heat up times will need to be increased hence the thought of changing controls for hw priority on a higher flow temp. Still running d.0 at 20kw and single zone at a time

 

[Chuck]

Given how much is being being built on the assumption, I'd want to check (using a stopwatch) and the gas meter, that the power the boiler claims to be delivering to the system matches the amount of gas being consumed.

 

[Timmy D]

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 🙂.