40kw Navien NCB Combi install with v.poor DHW? Is this adequate?

[ecswtrav]

You could also measure the actual shower flow rate with the shower temp control to minimum and on full flow, if temp setting is low enough ie a "cold" shower then no water will flow through the boiler, if this works then measure the actual shower flow rate with the shower at say 50C (or max) and the boiler at its minimum temp setting, this should then force all the water flow through the boiler and compare both flow rates.

Thanks for that. Little bit of progress...Navien are coming to see the boiler with the installer...not sure when yet but hopefully very soon so will be interesting to see what they say and whether they consider any testing like the above. Will definitely report back....

 

[ecswtrav]

A quick update as things are moving in the right direction at last and I'm grateful for the help here. Fitter came out and measured the flow rate at the boiler to be 20lpm. Navien visited earlier and the chap tried several new flow restrictor devices so as pointed out earlier in the discussion the flow restrictors within the boiler seem to be the culprit. It's now flowing at around 13-14lpm occasionally peaking briefly at 15lpm which is more on par with the spec for the 37kw boiler. The chap is going to investigate with Navien whether there is an alternative flow restrictor with a more open bore. I got the impression the thing he was showing me just couldn't be pulled out. Certainly progress though so thank you to those who have been extremely helpful. I'll update this if we manage to squeeze a few more lpm out of the boiler....I'm hoping so.

 

[ShaunCorbs]

Or maybe remove the flow restrictor and fit an external one on the hot out of the boiler etc ?

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[John.g]

Post #22 shows a link to restrictors which may be one of the ones installed in your boiler, they are orange, yellow and blue with respective flowrates of 25.5, 22.7 & 18.0 LPM at a minimum dynamic pressure of 2 bar, the outside tap pressure might give some idea with full usage.

 

[John.g]

Why do boilers need restrictors at all when the flowrate can be controlled at the end users?.

 

[ecswtrav]

Ran a few showers earlier and opened up a third outlet....the boiler was registering 18-18.5lpm so something has freed things up. It seems the more outlets open the higher the flow rate it registers Previously doing this I think got 10-11lpm maximum regardless of how many open.

A single outlet won't register 18lpm but the bath tap does 15lpm which is far better than when first installed and not far off what the istor kicked out. Assuming this is how a combi works so I think problem solved. Thank you to everyone for your help.