Is my Navien boiler behaving as expected?

[Oilyjoe]

Hi

Can you help me determine if my new Navien lcb700 lsx is working as expected?

I got the Navien oil boiler installed to replaced an old firebird boiler. The new boiler is a condensing oil boiler and I’m not sure if this is working as expected. I’ve a 300 L water cylinder and after one hour of heating the water temperature reaches 40-45C. The cylinder is less than a year old and the thermostat is working well.

When the heat demand is on, the boiler themostat is set to 60C. The burner starts and the boiler lcd panel reaches 60C. The burner will stop and the pump continues to run. When the temperature at the boiler drops to 40C, then the boiler will burn again to 60C. The cycle continues and the 60C to 40C drop takes about 20 minutes.

My question for anyone….is this normal?

Thanks

 

[ShaunCorbs]

Unvented cylinder?

 

[Oilyjoe]

Unvented cylinder?

Hi thanks

I somehow struggle to understand the difference. It’s a cylinder that is fed by a water tank in the attic, so I think it’s unvented. It’s a joule wellmaster 300L, controlled by a heatmister system and a 2 port valve.

Thanks for your help.

 

[ShaunCorbs]

That’s great do you know the size of the boiler kw ?

 

[Oilyjoe]

That’s great do you know the size of the boiler kw ?

28kw system oil navien lsx.

 

[ShaunCorbs]

As the coil on the cylinder is 22kw yes you will have some cycling also with the cylinder temp increasing this will also increase cycling/ time before it fires the boiler again

 

[Oilyjoe]

As the coil on the cylinder is 22kw yes you will have some cycling also with the cylinder temp increasing this will also increase cycling/ time before it fires the boiler again

Hi
Am I incorrect to expect the boiler to continue to fire until the water in the cylinder has reached the thermostat set temperature?

 

[ShaunCorbs]

Hi
Am I incorrect to expect the boiler to continue to fire until the water in the cylinder has reached the thermostat set temperature?

Yes or until the boiler is upto temp then it will wait until the temp drops below its threshold then refire and repeat

 

[Oilyjoe]

Yes or until the boiler is upto temp then it will wait until the temp drops below its threshold then refire and repeat

How long should a 28kw boiler take to heat a 300 L tank from say 20C to 60C?

 

[ShaunCorbs]

It will be around an hour due to the coil being miss matched

 

[Oilyjoe]

It will be around an hour due to the coil being miss matched

Hi
Cheers
My boiler won’t heat the temperature in the cyclinder from 30 to 60 within an hour. In fact, it won’t even manage this is 90 minutes.

Can you think of any reasons for this? It’s the only zone on at the time.

 

[ShaunCorbs]

Internal or external pump ?

 

[Oilyjoe]

Internal or external pump ?

The boiler is in the garage and the pump is within the boiler. The distance between boiler and cylinder is about 10m.

 

[ShaunCorbs]

Yea something isn’t right any chance of a picture of the airing cupboard?

 

[Oilyjoe]

Yea something isn’t right any chance of a picture of the airing cupboard?

 

[Oilyjoe]

Hi

Yes, my airing cupboard with my cylinder and the heatmister control area.

The 90 won’t heat the water when it is the only active zone.

Thanks

 

[ShaunCorbs]

There’s a red wheel headed valve above the ufh stuff is that open fully ?

You coil is big enough now due to you having a twin coil system in series

 

[Oilyjoe]

There’s a red wheel headed valve above the ufh stuff is that open fully ?

You coil is big enough now due to you having a twin coil system in series

Hi

Yes, this is fully open.

 

[ShaunCorbs]

Try closing it half way eg 3 turns

 

[Oilyjoe]

Try closing it half way eg 3 turns

Any other potential issues that could be responsible?

 

[ShaunCorbs]

Any other potential issues that could be responsible?

Could be supply pipes from the boiler not fully clear / restriction as I would say that coil would easy heat the cylinder up within the hour

 

[Oilyjoe]

Could be supply pipes from the boiler not fully clear / restriction as I would say that coil would easy heat the cylinder up within the hour

You might be right. The last boiler used 28mm pipe and this uses 22mm supply/return but connecting to the existing 28mm pipe into the house

 

[RoryD]

Wondering if the Pump is up to scratch?... 10m?