Vaillant boiler taking ages to get to target temperature

[b21playa]

Hi all

Wondering if you could help with this strange issue.

I have a Vaillant ecotec 637 (set to 20kw part load) which was connected via a LLH to my system of 3 zones; DHW and 2 radiator zones. The gas usage was high and didn’t feel the boiler was modulating, so yesterday I decided to remove the LLH and just connect directly to the boiler. I noticed today with the target temp of 75, the boiler was sat around 60 after an hour and even after a few hours it’s only just about got the 70degC. Also when initial heating called for the boiler modulates down to a small flame and takes a while for it to ramp up.

This is strange as with the LLH I never had this issue and easily got the target temp and stayed there. Now I know most likely I’ll need to refit the header, but wondered why the boiler doesn’t ramp up straight away?

Thanks in advance

 

[b21playa]

Just to add the ground floor has 10 rads and the upstairs circuit (1st and loft) has 8 rads. If both zones on, the boiler now won’t ever get to set temp and will sit around 57degc

 

[b21playa]

Just checked all rads, based on deltaT50 values upstairs circuit 14.8kw and downstairs 18.7kw. We run the heating at 70-75degC and have a very uninsulated house - needs new windows and loft insulation

 

[gmartine]

Is there a reason why boiler d0 set to partial load of 20kw when you've got a combined heating load of well over 30kw?

 

[b21playa]

Is there a reason why boiler d0 set to partial load of 20kw when you've got a combined heating load of well over 30kw?

Hi. Most of the time only 1 zone is on. With temps dropping have started to use both radiator zones.

 

[Brambles]

When you removed the LLH how have you reconfigured the pumps?

If configured incorrectly (pumping arrangement) it is probable that the boiler performance response is being limited by the temperature differential (high) across the heat exchanger

 

[b21playa]

When you removed the LLH how have you reconfigured the pumps?

I have removed the additional pump on the secondary side and just using boiler pump

 

[John.g]

If any one zone or/and a number of zones are > than 20kw then the boiler will hardly reach target temp?.
The reason it was with the LLH was possibly because the secondary (rad) flow was greater than the primary flow and was diluting ( by recirculating) the boier flow to give reduced rad inlet flows = reduced rad output.
what are d.40&d.41 values now?. You will have to increase d.00, there was a good reason for installing that LLH, wonder why you thought it was causing excessive gas consumption.

 

[John.g]

I have removed the additional pump on the secondary side and just using boiler pump

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

 

[b21playa]

If any one zone or/and a number of zones are > than 20kw then the boiler will hardly reach target temp?.
The reason it was with the LLH was possibly because the secondary (rad) flow was greater than the primary flow and was diluting ( by recirculating) the boier flow to give reduced rad inlet flows = reduced rad output.
what are d.40&d.41 values now?. You will have to increase d.00, there was a good reason for installing that LLH, wonder why you thought it was causing excessive gas consumption.

D40/41 is 57/44.

Maybe I just put the LLH back in

 

[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.