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Discuss 40kw Navien NCB Combi install with v.poor DHW? Is this adequate? in the Gas Engineers Forum area at PlumbersForums.net

ShaunCorbs

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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!

5l bucket or 1l bottle work well just time hoe long it takes to fill either and work it out how many you can fill in 60 seconds

for example if a 1l bottle takes 10 seconds to fill your running 6lpm etc if it takes 5 seconds it’s 12lm etc

you can do this via the filling loop will give an approximate gauge

eg turn the black lever off turn the blue lever off

disconnect the flex from the black lever side on the silver nut

put this into a 5l bucket or aim get your timer ready when ready open the blue lever fully and start timer etc
 
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5l bucket or 1l bottle work well just time hoe long it takes to fill either and work it out how many you can fill in 60 seconds

for example if a 1l bottle takes 10 seconds to fill your running 6lpm etc if it takes 5 seconds it’s 12lm etc

you can do this via the filling loop will give an approximate gauge

eg turn the black lever off turn the blue lever off

disconnect the flex from the black lever side on the silver nut

put this into a 5l bucket or aim get your timer ready when ready open the blue lever fully and start timer etc
Just followed your instructions nice and straightforward thanks. Although the boiler has a dedicated feed in 22mm pipe using that method I get spot on 9lpm....which corresponds nicely with the boiler readouts.
I gather this is why I'm not getting the desired flow rates?
 

ShaunCorbs

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Correct you have a restriction on the cold main somewhere need to follow this pipe all the way back to the main
 
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Just followed your instructions nice and straightforward thanks. Although the boiler has a dedicated feed in 22mm pipe using that method I get spot on 9lpm....which corresponds nicely with the boiler readouts.
I gather this is why I'm not getting the desired flow rates?

Don't want to be awkard but its strange that a open ended pipe via that flexible hose is only giving you 9LPM when you can get up to 12.5LPM from two HW taps, one of which is upstairs, and the water must also pass through the boiler heat exchanger.
 
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Correct you have a restriction on the cold main somewhere need to follow this pipe all the way back to the main
The Istor never suffered from this issue so could this issue possibly be installation related? Seems strange how all of a sudden the flow rate has dropped after installation of a new boiler. The Istor even had a prv limiting the pressure....this doesn't and have anything limiting on the supply line now. Just for reference too, I also popped outside and tried the cold tap again....approx 21/22lpm getting to that still.
 
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Don't want to be awkard but its strange that a open ended pipe via that flexible hose is only giving you 9LPM when you can get up to 12.5LPM from two HW taps, one of which is upstairs, and the water must also pass through the boiler heat exchanger.
Yeah I agree....the only time I've managed to get a higher flow rate reading on the boiler screen is when I've opened a few hot outlets. A single outlet stays around the 9-10 mark.
 
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Is the blue isolating valve just attached to the cold supply to the boiler and is that "1.5 bar" PG just monitoring the boiler system pressure?

Also check for a PRV installed somewhere on the cold feed to the boiler, it may be faulty because in order for the flow rate to increase from 9LPM to 12.6LPM would require a pressure increase from 2.2 bar to 4.3 bar for any fixed restriction/obstruction in the cold water feed.
 
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ShaunCorbs

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Don't want to be awkard but its strange that a open ended pipe via that flexible hose is only giving you 9LPM when you can get up to 12.5LPM from two HW taps, one of which is upstairs, and the water must also pass through the boiler heat exchanger.

but that would of had 22mm pipework and not 15mm so there’s a joint somewhere maybe an iso valve etc
 
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Maybe my thinking is wrong but a test was carried out on the cold feed supply only to the boiler by breaking a pipe (hose) so would expect the maximum possible flow rate from this as the cold feed is now open at one end, the same supply is then feeding the boiler, the hot water pipe or pipes to the hot taps and gives 40% more flow than flowing out the open end of the supply pipe.
The only other explanation is that the hot taps have mixers.
 
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Well, no contact from the fitter as yet although an electrician was here fitting some opentherm controls as part of the deal. Checked again at the outside tap and confirm it was still 22lpm. I did try the washing machine inlet hose and that didn't quite match the 22lpm and was around 17.5 but I think by looking it was really restrictive with a very tiny hole at the end. Either way it exceeded 9lpm.
Just a few feet upstream from the stopcock are the two isolation valves....one on the cold supply and the other on the boiler supply....so as suggested maybe the boiler supply one is faulty? I believe these were full bore when fitted. From looking they're both open it would seem fully.
The prv has been removed that was used to limit the istor boiler feed to 2 bar so there is nothing else on this feed to the boiler....just a left hand turn which then leads straight to the boiler.
The fitters have pieced back some plasterboard behind the boiler so I wonder if there is something restrictive they've fitted beyond this hidden out of sight?
John.g you are correct - the bathroom tap is a mixer tap.
I will keep this updated anyway until we get this resolved as I appreciate everyone's help.
 
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Sometime, you might try this.
What flowrate does the boiler show (1) if you ran the shower only, with the boiler temp at minimum of 35C and (2) with boiler temp at max temp where you will also have mixing.
 
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Sometime, you might try this.
What flowrate does the boiler show (1) if you ran the shower only, with the boiler temp at minimum of 35C and (2) with boiler temp at max temp where you will also have mixing.
I just gave that a try....ran the shower in the ensuite in the loft as that is the furthest away of the two. There was minimal difference for some reason and both temps hovered around the 5.8lpm mark on the boiler display....the lower temp exceeding it intermittently. The shower itself has a rain head and is perfectly usable at those flow rates but just not what we were used to.
 

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