New Boiler to replace a old Worcester 35CDi II

[ShaunCorbs]

And this was with the bath tap running just checking ?

 

[John.g]

If that's m3i in 2 mins then 0.04 in 2 mins = 1.2m3/hr approx 13kw or about 11kw at 85% efficiency. Bath tap 0n??

 

[ShaunCorbs]

11.59net (12.86gross)

 

[j3oeff]

And this was with the bath tap running just checking ?

No, kitchen one. Should it of been the bath tap? If so I'll do it in the morning now

 

[j3oeff]

If that's m3i in 2 mins then 0.04 in 2 mins = 1.2m3/hr approx 13kw or about 11kw at 85% efficiency. Bath tap 0n??

Kitchen tap on full.

 

[ShaunCorbs]

No, kitchen one. Should it of been the bath tap? If so I'll do it in the morning now

Yes please

 

[j3oeff]

Will in the morning. Thanks for helping with this chaps. Appreciate it and learning at the same time.

 

[John.g]

If these two (post31) then
12.09 secs @ 42.4c 4.96LPM, 12.07kw
18.10 secs @ 54.4c 3.31LPM, 10.83kw
Average 11.45kw

Very close to flow/temp calc??falls off with increasing temp

Might be something to do with combi temp control? as output decreases with increasing HW temp and boiler gets close to rated output at reducing temps.

 

[John.g]

Had a look at the Baxi830 manual, it states minimum flowrate 2 LPM but recommend 2.5 LPM and the minimum output is 6.1kw.
The lowest test flow reading was 2.74LPM (bathroom tap) which gave a measured temp of 41.1C from mains at 7.5C = 6.42kw.
With the DHW temp control to max, 60C, and if the measured HW temp was 60C, then 10.04kw required so no reason why the boiler shouldn't have achieved this.

 

[j3oeff]

Some more 2 minute hot tap runs with readings.

Bath start 383,730 finish 383,812
Main bathroom sink tap start 383,812 finish 383,894
Ensuite sink tap start 383,894 finish 383,973
Ensuite shower set at 38c start 383,973 finish 384,028

 

[j3oeff]

If these two (post31) then
12.09 secs @ 42.4c 4.96LPM, 12.07kw
18.10 secs @ 54.4c 3.31LPM, 10.83kw
Average 11.45kw

Very close to flow/temp calc??falls off with increasing temp

Might be something to do with combi temp control? as output decreases with increasing HW temp and boiler gets close to rated output at reducing temps.

They are both kitchen tap readings which is directly next to the boiler. That tap is certainly the hottest and the only one where you wouldn't be able to keep your hand under at the correct flow to achieve the hottest water.

 

[ShaunCorbs]

Bath 23.76 kw
Mbst 23.76 kw
Est 22..89 kw
Ess 15.94 kw

And your getting around 12 lpm out of the bathroom and sink taps if you are boiler fault as the top two should be 30kw

 

[j3oeff]

Bath 23.76 kw
Mbst 23.76 kw
Est 22..89 kw
Ess 15.94 kw

And your getting around 12 lpm out of the bathroom and sink taps if you are boiler fault as the top two should be 30kw

Am I right in reading that as.... There is a fault with the boiler if those readings I give are correct?

 

[ShaunCorbs]

If you have 12 lpm coming out of the tap then yes

 

[j3oeff]

If you have 12 lpm coming out of the tap then yes

All taps were on full when tests were done so it will be correct. Will a boiler reset achieve anything or am I best off calling baxi as you said previously. ta

 

[John.g]

Some more 2 minute hot tap runs with readings.

Bath start 383,730 finish 383,812
Main bathroom sink tap start 383,812 finish 383,894
Ensuite sink tap start 383,894 finish 383,973
Ensuite shower set at 38c start 383,973 finish 384,028

From post#31 (below) My calcs in bold.
Bathroom ensuite
12.82 secs @ 39.4c 4.48LPM 9.97kw
20.31 secs @ 43.1c 2.96LPM 7.35kw
Main bathroom sink
12.51 secs @ 35.1c 4.79LPM, 9.22kwkw
21.83 secs @ 41.1c 2.74LPM, 6.44kw
From post #62 (Shaun)
Bath 23.76 kw
Mbst 23.76 kw
Est 22..89 kw
Ess 15.94 kw

Which, if any, of the above (Shaun) taps correspond to the post #31 taps (Ignore power outputs)

Edit: Also, if the shower temp was actually 38C then a boiler output of 15.94kw gives flowrate of 7.5LPM

 

[j3oeff]

From post#31 (below) My calcs in bold.
Bathroom ensuite
12.82 secs @ 39.4c 4.48LPM 9.97kw
20.31 secs @ 43.1c 2.96LPM 7.35kw
Main bathroom sink
12.51 secs @ 35.1c 4.79LPM, 9.22kwkw
21.83 secs @ 41.1c 2.74LPM, 6.44kw
From post #62 (Shaun)
Bath 23.76 kw
Mbst 23.76 kw
Est 22..89 kw
Ess 15.94 kw

Which, if any, of the above (Shaun) taps correspond to the post #31 taps (Ignore power outputs)

Now....in simple terms what does this mean? I get the LPM but don't understand the kw readings and what it all means in comparison to my iasue. But I assume the LPM is irrelevant if we are not getting the required HW output?

 

[ShaunCorbs]

You should be getting 12lpm and 30kw

 

[j3oeff]

You should be getting 12lpm and 30kw

Crikey, so some way off then on all of the upstairs outlets.

 

[John.g]

One is a check on the other.

IF the measured flowrates and temperatures are correct then the calculated boiler output can a is very accurately calculated.

Now....in simple terms what does this mean? I get the LPM but don't understand the kw readings and what it all means in comparison to my iasue. But I assume the LPM is irrelevant if we are not getting the required HW output?

A bit long winded but....
From one of your readings above of 1 litre fill in 12.82 secs and 39.4C then this equals to a flowrate of 60/12.82, 4.68LPM and the water must be raised in temperature from 7.5C to 39.4C, a dT of 31.9C.
The well know calc for the energy required is kw= LPMX60XdT/860, in this case, 4.68X60X31.9/860, 10.42kw. this will be IMO almost100% correct, as a check you can take the gas meter readings, these readings in M3 can be converted to the boiler output required or visa versa in our case, I don't know the exact conversion factors but if you use 10.8kw/M3 of gas and a boiler efficiency of say 88% then you won't be far out .
So, gas consumption in M3/hr is 10.42/10.8/0.88, 1.096M3/hr or 0.0365M3/2mins. So if both of these calcs marry up then you are happy but either one will give be almost 100% correct.

 

[j3oeff]

One is a check on the other.

IF the measured flowrates and temperatures are correct then the calculated boiler output can a is very accurately calculated.



A bit long winded but....
From one of your readings above of 1 litre fill in 12.82 secs and 39.4C then this equals to a flowrate of 60/12.82, 4.68LPM and the water must be raised in temperature from 7.5C to 39.4C, a dT of 31.9C.
The well know calc for the energy required is kw= LPMX60XdT/860, in this case, 4.68X60X31.9/860, 10.42kw. this will be IMO almost100% correct, as a check you can take the gas meter readings, these readings in M3 can be converted to the boiler output required or visa versa in our case, I don't know the exact conversion factors but if you use 10.8kw/M3 of gas and a boiler efficiency of say 88% then you won't be far out .
So, gas consumption in M3/hr is 10.42/10.8/0.88, 1.096M3/hr or 0.0365M3/2mins. So if both of these calcs marry up then you are happy but either one will give be almost 100% correct.

Understand the logic of getting the figures now, thanks.

The gas readings were as you say M3. I'll ring baxi/plumber in the new year and get them to come out to it to try and find out exactly what the issue is.

 

[John.g]

You can see that the boiler just isn't giving anywhere near the required output if the DHW temp is set to 60C.
Take your own example again, above, you have a flowrate of 4.68LPM and you require a flowtemp of 60C (because that is what the max boiler DHW temp is) a dT of (60-7.5), 52.5C.
Boiler output required is 4.68X60X52.5/860, 17.14kw but you are only achieving a flowtemp of 39.4C (and a boiler output of 10.42kw). IF the boiler DHW temp had been set to 39.4C then, yes, you will get a flowrate of 4.68LPM at 39.4C but the settting is cranked up to max of 60C?. Really no need IMO but certainly no harm, to confirm with gas meter.

 

[j3oeff]

You can see that the boiler just isn't giving anywhere near the required output if the DHW temp is set to 60C.
Take your own example again, above, you have a flowrate of 4.68LPM and you require a flowtemp of 60C (because that is what the max boiler DHW temp is) a dT of (60-7.5), 52.5C.
Boiler output required is 4.68X60X52.5/860, 17.14kw but you are only achieving a flowtemp of 39.4C (and a boiler output of 10.42kw). IF the boiler DHW temp had been set to 39.4C then, yes, you will get a flowrate of 4.68LPM at 39.4C but the settting is cranked up to max of 60C?. Really no need IMO but certainly no harm, to confirm with gas meter.

I assume it could be a number of things could be why it is not giving the correct output? Or will it be easy to narrow down running some basic in house tests? Can I do the gas tests to confirm? I thought that's what the m3 readings were? Ta

 

[ShaunCorbs]

The taps have some influence on flow rate if there modern they might have flow restrictors in etc hence bath taps giving the full amount

 

[j3oeff]

The taps have some influence on flow rate if there modern they might have flow restrictors in etc hence bath taps giving the full amount

I'm pretty sure they do have flow restrictors in them but not the bath as you say. But that still doesn't explain the lack of temperature at the bath taps does it? You certainly shouldn't be filling a bath or sink with hot water and not need to add cold to it. I can only think there's an issue with the boiler/install as it was giving red hot water previously at all taps apart from bath where it would go cold after a while which I put down to the old broken boiler as when we moved in it was fine.