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

[John.g]

I would think, if installed, that they can certainly be removed.
It shows a differential pressure of ~ 2 bar is required for a flow rate of 20 LPM so would probably need 3 bar mains pressure to give 1 bar at the boiler inlet,
at 12 lpm the deltaP required is ~ 0.9 bar so the mains pressure would be ~ 2 bar at this flowrate to give 1 bar at the boiler inlet., these restrictors, if fitted, can have a very significant effect on the final flowrate IMO.

 

[ecswtrav]

I would think, if installed, that they can certainly be removed.
It shows a differential pressure of ~ 2 bar is required for a flow rate of 20 LPM so would probably need 3 bar mains pressure to give 1 bar at the boiler inlet,
at 12 lpm the deltaP required is ~ 0.9 bar so the mains pressure would be ~ 2 bar at this flowrate to give 1 bar at the boiler inlet., these restrictors, if fitted, can have a very significant effect on the final flowrate IMO.

Had a quick look at the manual I have here and there's no mention of flow restrictors just something about cleaning the return adaptor filter on page 51 which I assume isn't it? I've attached the manual it would be great if you had a sec to see if there's anything obvious that could have been missed. I'm going to try at some point today to measure the mains pressure just after the stopcock just so I can be sure what pressure is coming in. Thanks

 

[John.g]

I don't see any reference to cold water restrictors but on page 23 it states "After installing the boiler clean the cold water inlet filter", this of course may only refer to a typical installation but it is mentioned.

Re monitoring pressure, you have a 3 bar PG at the outside tap so when no flow through it but with flow through the combi should tell you something as it should reflect any pressure drop at the mains, just switch in the DHW and watch it, you really want another PG somewhere at the end of hot water supply to the house. Also even though it shouldn't have any effect on the flow through the boiler turn up the DHW temp control knob to max while doing the tests.

What was the kw output of your old Istor? did flow rate feel ok?

 

[ecswtrav]

I don't see any reference to cold water restrictors but on page 23 it states "After installing the boiler clean the cold water inlet filter", this of course may only refer to a typical installation but it is mentioned.

Re monitoring pressure, you have a 3 bar PG at the outside tap so when no flow through it but with flow through the combi should tell you something as it should reflect any pressure drop at the mains, just switch in the DHW and watch it, you really want another PG somewhere at the end of hot water supply to the house. Also even though it shouldn't have any effect on the flow through the boiler turn up the DHW temp control knob to max while doing the tests.

What was the kw output of your old Istor? did flow rate feel ok?

I will clarify the page 23 with the installer so thanks. I've just attached the PG to the point just after the stopcock....today around 15 mins ago it measured 2.2bar. Assuming it must fluctuate if I got 3 bar previously an outside tap. (The outside tap was the same 2.2bar btw) cranked up the boiler temp to maximum 65 degrees and opened a few outlets. The PG changed to 2bar lowest...it didn't move much at all. I'm not sure what this means I'll be honest, I just can't figure a way of measuring the pressure beyond the boiler although hopefully my fitter will have something for this. If I felt confident at removing the filling loop I'd try and measure the flow rate before it hits the boiler.
The Istor I believe was 24kw but with the pressurised cylinder we had much better flow from the taps....particulalry the hot bath tap...a massive difference...and the showers were more powerful.

 

[John.g]

It means basically that the mains pressure is fluctuating between 3 bar and 2.2 bar due to other users or whatever but your demand of 12 LPM or whatever is only dropping it a further 0.2bar (no problem from that point of view but 2 bar is IMO a pretty poor pressure for combi boiler flow rate performance). The outside tap (when not in use) will measure the mains pressure. The filling loop PG can only be utilized if the cold supply to it is from the same cold supply as to the combi, you must then be able to shut off the PRV outlet to the boiler, then screw down the PRV adjuster to reflect the mains pressure, a bit messy IMO, if you can use your own PG and attach it to the cold take off then open up your hot taps, you will then measure the pressure loss in the 40ft of cold pipe between the mains and the boiler inlet which I expect to be very low but worth taking to rule it in/out. I would then remove the gauge and re install it on the HW outlet, as close to the boiler as possible but this will have to be done with a Tee, then remove it and Tee in in to one one of HW users with the greatest flow and repeat the the test, your plumber might have to do these tests for you.

 

[gmartine]

I looked at the data tables and they specify 12.71 l/m @ 45 degrees for the "kitchen outlet" that happens to be what the OP is getting as a flow rate. Might not be relevant but thought it was odd.

 

[John.g]

That was from two taps.***. "Just opened two hot taps - one in a sink next to the boiler and one in a sink upstairs in the kitchen (boiler in basement). kitchen was 5.4lpm and basement tap 7.2lpm" so kitchen was 5.4 LPM.

Would like to know the deltaP through its plate Hx or through any combi for that matter.
The old boiler, not sure if a combi but with a HW cylinder as well was giving much better flow rates through the showers and HW taps and it was the same cold water line supply so the only big change is the boiler itself?.

 

[ecswtrav]

That was from two taps.***. "Just opened two hot taps - one in a sink next to the boiler and one in a sink upstairs in the kitchen (boiler in basement). kitchen was 5.4lpm and basement tap 7.2lpm" so kitchen was 5.4 LPM.

Would like to know the deltaP through its plate Hx or through any combi for that matter.
The old boiler, not sure if a combi but with a HW cylinder as well was giving much better flow rates through the showers and HW taps and it was the same cold water line supply so the only big change is the boiler itself?.

Was hoping to reply this eve with some info from Navien as I was contacted today by the boiler fitting company saying the installer had spoken to Navien earlier today. No phonecall as yet so I can't really update.
Yes previously the ideal istor was an all in one unit of a 24kw system boiler (an icos or something similar) attached to an unvented cylinder. It had a prv at the mains set to 2bar which has since been replaced with a straight pipe and the flow from taps was far superior. I never did take any measurement but a bath would fill up in no time....now I'm sitting around for a while longer. Cold tap is no different than previously so no issues with the cold supply.
All the same pipework other than the 22mm pipe serving the boiler has been reduced to 15mm where it connects and the prv removed so pressure now makes its way up to 3bar. I've attached a pic...assuming it all looks ok?
The gas supply crossed my mind just simply with it being a bigger KW boiler but probably thinking on a bit of a simplistic level for that justification.
Thanks

 

[ShaunCorbs]

Have you tested the lpm at the boiler yet ?

 

[John.g]

Was hoping to reply this eve with some info from Navien as I was contacted today by the boiler fitting company saying the installer had spoken to Navien earlier today. No phonecall as yet so I can't really update.
Yes previously the ideal istor was an all in one unit of a 24kw system boiler (an icos or something similar) attached to an unvented cylinder. It had a prv at the mains set to 2bar which has since been replaced with a straight pipe and the flow from taps was far superior. I never did take any measurement but a bath would fill up in no time....now I'm sitting around for a while longer. Cold tap is no different than previously so no issues with the cold supply.
All the same pipework other than the 22mm pipe serving the boiler has been reduced to 15mm where it connects and the prv removed so pressure now makes its way up to 3bar. I've attached a pic...assuming it all looks ok?
The gas supply crossed my mind just simply with it being a bigger KW boiler but probably thinking on a bit of a simplistic level for that justification.
Thanks

The gas supply has nothing to do with the flow rate, you could have the boiler switched off and it won't affect the flow rate. A 20kw combi can give the same flowrate as a 40kw, it just wont be as hot.

 

[ecswtrav]

Have you tested the lpm at the boiler yet ?

I'm going to ask the fitter to do this for me as I'm a bit uncertain how to go about it. Funnily enough I did ask him to do this during the installation before connecting up the boiler but he didn't have a flow cup on the van!

 

[John.g]

Basically what is required is to measure the flow coming out of the boiler to see if there is some fault/restriction in the boiler so simply put, disconnect the outlet from the boiler, turn the temperature control to minimum, (despite what I said you do I think need the boiler diverter valve to DHW) and let the water flow into a bucket for a timed period of one minute and just measure this with anything handy like a one litre jug.