Vaillant boiler taking ages to get to target temperature

[b21playa]

Is the LLH removed and the boiler flow/return connected as in no LLH?.

Yes LLH totally removed and piped as if it was never there, pictures added

 

[John.g]

Why not just increase d.00 to say 30kw??.

 

[b21playa]

Why not just increase d.00 to say 30kw??.

Downstairs circuit is say 19kw and main one used, thought 20kw would be sufficient. I was trying to reduce gas usage, wouldn’t this just increase it. Could this be the reason for slow ramp up?

Also looking at the picture, is the LLH connected right way around?

 

[John.g]

It will only increase it to the level required to give the rated output of the rads, if you increased d.00 to 30kw and reduced the boiler target temp to 57/60C then you will burn the same amount of gas as just now but you are limiting the rad output which may be fine as you will get better condensing, of course if you put another zone in service then obviously higher fuel consumption but you can't have it both ways.

 

[John.g]

Also looking at the picture, is the LLH connected right way around?

I think so, yes.

 

[b21playa]

I think so, yes.

Thank you. I see your point about increasing to 30kw and changing set point, but it will mean output to rads will be less which I don’t want. I think I’ll stick the LLH back in later. That way I know it heats up quicker and the secondary pump has a better head rate.

I was told previously that my boiler was oversized and would of been better with a 624 with d.0 set to auto

 

[John.g]

You have a total rad demand (2 zones on) of 33.5kw so how can a 624 service both?.
Before you reinstall that LLH, can you put the 2 zones in service with d.0 at 30kw and just take d.40&d.41.

Also remember that (probably) originally, the secondary flowrate was set up for both zones so, when one zone only in service, then the flow temperature to these rads will be greately reduced leading to reduced output but that is a "feature" of LLHs, it would be useful to install even a clamp on thermometer on the secondary flow pipe at the LLH, you can quickly determine the pump settings for both one/two zones to give optimum performance/economy.

Didn't you install this about a year ago??.

 

[b21playa]

You have a total rad demand (2 zones on) of 33.5kw so how can a 624 service both?.
Before you reinstall that LLH, can you put the 2 zones in service with d.0 at 30kw and just take d.40&d.41.

Also remember that (probably) originally, the secondary flowrate was set up for both zones so, when one zone only in service, then the flow temperature to these rads will be greately reduced leading to reduced output but that is a "feature" of LLHs, it would be useful to install even a clamp on thermometer on the secondary flow pipe at the LLH, you can quickly determine the pump settings for both one/two zones to give optimum performance/economy.

Didn't you install this about a year ago??.

Yes I can try that, how long shall I run it before getting d.40/d.41

I have a clamp on thermometer I can check with once reinstalled.

Yes was installed last year, since then I’ve had additional rads added/replaced

 

[John.g]

W w w w w w,tw,ww ww,r,

Yes I can try that, how long shall I run it before getting d.40/d.41

I have a clamp on thermometer I can check with once reinstalled.

Yes was installed last year, since then I’ve had additional rads added/replaced

Run them until the flow temp is say 65C.

 

[b21playa]

W w w w w w,tw,ww ww,r,
Run them until the flow temp is say 65C.

Finally got to 65, it was 65/47