New Boiler to replace a old Worcester 35CDi II

[j3oeff]

Here are preliminary calculations, awaiting mains temperature but probably won't make a huge difference.

		DHW​	Boiler​
	Mains​	Setpoint​	Rated​			​
	Temp​	Temp​	Output​			​
	DegC​	DegC​	KW​			​
	12​	60​	30​			​
	Downstairs​					​
	Bathroom​	Measured​	Achievable​	Required​	Actual​	​
	Tap​	Temp​	Temp​	Output​	Output​	​
Bath sink​	LPM​	DegC​	DegC​	KW​	KW​	​
7.12 - 52.4c​	8.4​	52.4​	60.0​	28.2​	23.8​	​
6.98 - 54.7c​	8.6​	54.7​	60.0​	28.8​	25.6​	​
	8.5​	53.6​	60.0​	28.5​	24.7​	Average​
	Ensuite​
	Sink​	Measured​	Achievable​	Required​	Actual​
	Tap​	Temp​	Temp​	Output​	Output​
Ensuite​	LPM​	DegC​	DegC​	KW​	KW​
8.39 - 56.4c​	7.2​	56.4​	60.0​	23.9​	22.2​
9.10 - 53c​	6.6​	53.0​	60.0​	22.1​	18.9​
	6.9​	54.7​	60.0​	23.0​	20.5​	Average​
	Bath​	Measured​	Achievable​	Required​	Actual​
	Tap​	Temp​	Temp​	Output​	Output​
Bath tap​	LPM​	DegC​	DegC​	KW​	KW​
6.11 - 53.7c​	9.82​	53.7​	55.8​	30.0​	28.6​	​
7.67 - 48.4c​	7.82​	48.4​	67.0​	30.0​	19.9​	​
	8.82​	51.05​	60.7​	30.0​	24.2​	Average​

I've noticed the jug fills have taken longer and some are a little less LPM. Any reason for that? One thing i use to get with the old boiler when turning the hot taps on upstairs was a clunk type noise which sounded like something was kicking in and hot water started flowing.

That went away when new boiler was installed but has for some reason now returned. Odd

 

[ShaunCorbs]

He hasn’t slightly closed the 2nd in from the right going from right to left has he ?

 

[John.g]

Final calculations, cold mains, 7.0C.

Definitely appears a (good) bit shy of full output, say 5/6kw, which may need verifying with gas meter monitoring, I wouldn't be too happy with the above to be honest as you might only effectively have a 24/25 kw shower.

You might also do the bath tap at its full output of ~ 14LPM.

Re Shower: IF the boiler output was/is 30kw then you will get 10.0 LPM at 50C. (from cold at 7C)
If the boiler output is indeed say 25kw then you will get 8.3LPM
or at a showering temp of 40C, the numbers are 13.03LPM & 10.9LPM.
Suggest you measure the flow and temperature from the shower as well.

		DHW​	Boiler​
	Mains​	Setpoint​	Rated​			​
	Temp​	Temp​	Output​			​
	DegC​	DegC​	KW​			​
	7​	60​	30​			​
	Downstairs​					​
	Bathroom​	Measured​	Achievable​	Required​	Actual​	​
	Tap​	Temp​	Temp​	Output​	Output​	​
Bath sink​	LPM​	DegC​	DegC​	KW​	KW​	​
7.12 - 52.4c​	8.4​	52.4​	58.0​	30.0​	23.8​	​
6.98 - 54.7c​	8.6​	54.7​	57.0​	30.0​	25.6​	​
	8.5​	53.6​	57.5​	30.0​	24.7​	Average​
	Ensuite​
	Sink​	Measured​	Achievable​	Required​	Actual​
	Tap​	Temp​	Temp​	Output​	Output​
Ensuite​	LPM​	DegC​	DegC​	KW​	KW​
8.39 - 56.4c​	7.2​	56.4​	60.0​	26.4​	22.2​
9.10 - 53c​	6.6​	53.0​	60.0​	24.4​	18.9​
	6.9​	54.7​	60.0​	25.4​	20.5​	Average​
	​	Measured​	Achievable​	Required​	Actual​	​
	Kitchen​	Temp​	Temp​	Output​	Output​	​
kitchen​	LPM​	DegC​	DegC​	KW​	KW​	​
10.90 - 57.5c	5.5​	57.3​	60​	18.4​	17.4​	​
10.77 - 57c	5.6​	57​	60​	18.7​	17.5​	​
	5.5​	57.2​	60.0​	18.5​	17.4​	Average​
	Bath​	Measured​	Achievable​	Required​	Actual​
	Tap​	Temp​	Temp​	Output​	Output​
Bath tap​	LPM​	DegC​	DegC​	KW​	KW​
6.11 - 53.7c​	9.82​	53.7​	50.8​	30.0​	28.6​	​
7.67 - 48.4c​	7.82​	48.4​	62.0​	30.0​	19.9​	​
	8.82​	51.05​	55.7​	30.0​	24.2​	Average​

 

[John.g]

I presume thermostatic showers have a flow control "knob" as well as the temperature setting, because if not then if the thermostat is closing off the cold water completely, as it should, the temp can still be too low depending on the hot flowrate through the shower and the boiler output?.
So maybe nothing wrong with the thermostatic control?.

 

[j3oeff]

Final calculations, cold mains, 7.0C.

Definitely appears a (good) bit shy of full output, say 5/6kw, which may need verifying with gas meter monitoring, I wouldn't be too happy with the above to be honest as you might only effectively have a 24/25 kw shower.

You might also do the bath tap at its full output of ~ 14LPM.

Re Shower: IF the boiler output was/is 30kw then you will get 10.0 LPM at 50C. (from cold at 7C)
If the boiler output is indeed say 25kw then you will get 8.3LPM
or at a showering temp of 40C, the numbers are 13.03LPM & 10.9LPM.
Suggest you measure the flow and temperature from the shower as well.

		DHW​	Boiler​
	Mains​	Setpoint​	Rated​			​
	Temp​	Temp​	Output​			​
	DegC​	DegC​	KW​			​
	7​	60​	30​			​
	Downstairs​					​
	Bathroom​	Measured​	Achievable​	Required​	Actual​	​
	Tap​	Temp​	Temp​	Output​	Output​	​
Bath sink​	LPM​	DegC​	DegC​	KW​	KW​	​
7.12 - 52.4c​	8.4​	52.4​	58.0​	30.0​	23.8​	​
6.98 - 54.7c​	8.6​	54.7​	57.0​	30.0​	25.6​	​
	8.5​	53.6​	57.5​	30.0​	24.7​	Average​
	Ensuite​
	Sink​	Measured​	Achievable​	Required​	Actual​
	Tap​	Temp​	Temp​	Output​	Output​
Ensuite​	LPM​	DegC​	DegC​	KW​	KW​
8.39 - 56.4c​	7.2​	56.4​	60.0​	26.4​	22.2​
9.10 - 53c​	6.6​	53.0​	60.0​	24.4​	18.9​
	6.9​	54.7​	60.0​	25.4​	20.5​	Average​
	​	Measured​	Achievable​	Required​	Actual​	​
	Kitchen​	Temp​	Temp​	Output​	Output​	​
kitchen​	LPM​	DegC​	DegC​	KW​	KW​	​
10.90 - 57.5c	5.5​	57.3​	60​	18.4​	17.4​	​
10.77 - 57c	5.6​	57​	60​	18.7​	17.5​	​
	5.5​	57.2​	60.0​	18.5​	17.4​	Average​
	Bath​	Measured​	Achievable​	Required​	Actual​
	Tap​	Temp​	Temp​	Output​	Output​
Bath tap​	LPM​	DegC​	DegC​	KW​	KW​
6.11 - 53.7c​	9.82​	53.7​	50.8​	30.0​	28.6​	​
7.67 - 48.4c​	7.82​	48.4​	62.0​	30.0​	19.9​	​
	8.82​	51.05​	55.7​	30.0​	24.2​	Average​

Shower set at 50 on tap
6.68 - 35c

Shower set at 45 on tap
6.74 - 35.1c

Shower set at 38 on tap
6.40 - 35.1c

Are you saying I could still achieve hotter water of the boiler was outputting 5/6kwh more. How would I measure the gas readings to investigate further if so?

 

[j3oeff]

He hasn’t slightly closed the 2nd in from the right going from right to left has he ?

The pressure switch?

 

[John.g]

Shower set at 50 on tap
6.68 - 35c

Shower set at 45 on tap
6.74 - 35.1c

Shower set at 38 on tap
6.40 - 35.1c

Are you saying I could still achieve hotter water of the boiler was outputting 5/6kwh more. How would I measure the gas readings to investigate further if so?

As before, open the hot bath tap fully, measure its flowrate&temp, then leave it running and monitor the gas meter readings for exactly 2 minutes again.

 

[j3oeff]

As before, open the hot bath tap fully, measure its flowrate&temp, then leave it running and monitor the gas meter readings for exactly 2 minutes again.

Ok. will do tomorrow and come back with findings.

 

[ShaunCorbs]

The pressure switch?

The iso under neath the boiler eg black lever

2nd one in from the right side 15mm

 

[John.g]

Shower calcs attached,

			DHW	Boiler
		Mains	Setpoint	Rated
		Temp	Temp	Output
		DegC	DegC	KW
		7	60	30
		Downstairs
		Bathroom	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Bath sink	LPM	DegC	DegC	KW	KW
	7.12 - 52.4c	8.4	52.4	58.0	30.0	23.8
	6.98 - 54.7c	8.6	54.7	57.0	30.0	25.6
		8.5	53.6	57.5	30.0	24.7	Average
		Ensuite
		Sink	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Ensuite	LPM	DegC	DegC	KW	KW
	8.39 - 56.4c	7.2	56.4	60.0	26.4	22.2
	9.10 - 53c	6.6	53.0	60.0	24.4	18.9
		6.9	54.7	60.0	25.4	20.5	Average
			Measured	Achievable	Required	Actual
		Kitchen	Temp	Temp	Output	Output
	kitchen	LPM	DegC	DegC	KW	KW
	10.90 - 57.5c	5.5	57.3	60	18.4	17.4
	10.77 - 57c	5.6	57	60	18.7	17.5
		5.5	57.2	60.0	18.5	17.4	Average
		Bath	Measured	Achievable	Required	Actual
		Tap	Temp	Temp	Output	Output
	Bath tap	LPM	DegC	DegC	KW	KW
	6.11 - 53.7c	9.82	53.7	50.8	30.0	28.6
	7.67 - 48.4c	7.82	48.4	62.0	30.0	19.9
		8.82	51.05	55.7	30.0	24.2	Average
			Measured	Required	Required	Actual
		Shower	Temp	Temp	Output	Output
		LPM	DegC	DegC	KW	KW
Shower. SP 50C	6.68 - 35c	8.98	35.0	50.0	26.9	14.4
Shower. SP 45C	6.74 - 35.1c	8.90	35.1	45.0	23.6	14.3
Showr. SP 38C	6.4 - 35.1c	9.38	35.1	38.0	20.3	15.1
		9.09	35.07	44.33	23.61	14.62	Average

 

[John.g]

Corrected calculations (done at 12C) should have been 7C.

Looking a lot better now, so checks tomorrow will verify.

Shower discrepancies probably due to mixing problems, thermostat etc, to be determined.

			DHW​	Boiler​
		Mains​	Setpoint​	Rated​			​
		Temp​	Temp​	Output​			​
		DegC​	DegC​	KW​			​
		7​	60​	30​			​
		Downstairs​					​
		Bathroom​	Measured​	Achievable​	Required​	Actual​	​
		Tap​	Temp​	Temp​	Output​	Output​	​
	Bath sink​	LPM​	DegC​	DegC​	KW​	KW​	​
	7.12 - 52.4c​	8.4​	52.4​	58.0​	30.0​	26.7​	​
	6.98 - 54.7c​	8.6​	54.7​	57.0​	30.0​	28.6​	​
		8.5​	53.6​	57.5​	30.0​	27.6​	Average​
		Ensuite​
		Sink​	Measured​	Achievable​	Required​	Actual​
		Tap​	Temp​	Temp​	Output​	Output​
	Ensuite​	LPM​	DegC​	DegC​	KW​	KW​
	8.39 - 56.4c​	7.2​	56.4​	60.0​	26.4​	24.6​
	9.10 - 53c​	6.6​	53.0​	60.0​	24.4​	21.2​
		6.9​	54.7​	60.0​	25.4​	22.9​	Average​
		​	Measured​	Achievable​	Required​	Actual​	​
		Kitchen​	Temp​	Temp​	Output​	Output​	​
	kitchen​	LPM​	DegC​	DegC​	KW​	KW​	​
	10.90 - 57.5c	5.5​	57.3​	60.0​	20.4​	19.3​	​
	10.77 - 57c	5.6​	57​	60​	20.6​	19.4​	​
		5.5​	57.2​	60.0​	20.5​	19.4​	Average​
		Bath​	Measured​	Achievable​	Required​	Actual​
		Tap​	Temp​	Temp​	Output​	Output​
	Bath tap​	LPM​	DegC​	DegC​	KW​	KW​
	6.11 - 53.7c​	9.82​	53.7​	50.8​	30.0​	32.0​	​
	7.67 - 48.4c​	7.82​	48.4​	62.0​	30.0​	22.6​	​
		8.82​	51.05​	55.7​	30.0​	27.3​	Average​
		​	Measured​	Achievable​	Required​	Actual​
		Shower​	Temp​	Temp​	Output​	Output​
		LPM​	DegC​	DegC​	KW​	KW​
Shower. SP 50C​	6.68 - 35c​	8.98​	35.0​	54.9​	30.0​	17.5​	​
Shower. SP 45C​	6.74 - 35.1c​	8.90​	35.1​	55.3​	30.0​	17.5​	​
Showr. SP 38C​	6.4 - 35.1c​	9.38​	35.1​	52.9​	30.0​	18.4​	​
		9.09​	35.07​	54.35​	30.00​	17.79​	Average​

 

[j3oeff]

Bath tap run today

6.45 - 48c
6.36 - 48.5c
6.11 - 48.6c

Full 2 minute tap run

Gas reading start - 456.228
Gas reading finish - 456.372

 

[j3oeff]

The iso under neath the boiler eg black lever

2nd one in from the right side 15mm

Nothing looks closer to me?

 

[John.g]

4 min gas readings, 456.372-456.228 = 0.144 = 2.16M3/hr = 2.16*11.3. 24.41Kwh
Assume boiler efficiency at 90% = boiler output of 24.41*0.9 = 21.97kwh (22kw output boiler)
but your retested bath tap calculations show a calculated requirement of 27.5Kw so something not adding up here, you were able to get flow rates of ~ 14LPM from the bath tap a few days ago, so why not now?.

Bath tap

4.12 - 31.7c

4.27 - 34.6c

60/4.12 = 14.56LPM. 60/14.05LPM.
We have to be absolutely sure that the HW demand is well > than the boiler output and then do the gas meter check again
SO, either get a set of readings from the bath tap full open but if you cannot get more than the 8.9LPM at todays test, just open another hot tap, take the readings from both taps, let both taps open and do your 2 minute gas meter test again and that will finally prove the boiler output.
Also for accuracy, have a look at one of your gas bills and note the gas usage in M3, the gas usage is also converted to Kwh so divide the Kwh by the M3 used and that will give the Kwh/M3. I am using 11.3kwh/M3 from some user on another thread here.

			DHW​	Boiler​
		Mains​	Setpoint​	Rated​			​
		Temp​	Temp​	Output​			​
		DegC​	DegC​	KW​			​
		7​	60​	30​			​
		Downstairs​					​
		Bathroom​	Measured​	Achievable​	Required​	Calcul​	​
		Tap​	Temp​	Temp​	Output​	Output​	​
	Bath sink​	LPM​	DegC​	DegC​	KW​	KW​	​
	7.12 - 52.4c​	8.4​	52.4​	58.0​	30.0​	26.7​	​
	6.98 - 54.7c​	8.6​	54.7​	57.0​	30.0​	28.6​	​
		8.5​	53.6​	57.5​	30.0​	27.6​	Average​
		Ensuite​
		Sink​	Measured​	Achievable​	Required​	Calcul​
		Tap​	Temp​	Temp​	Output​	Output​
	Ensuite​	LPM​	DegC​	DegC​	KW​	KW​
	8.39 - 56.4c​	7.2​	56.4​	60.0​	26.4​	24.6​
	9.10 - 53c​	6.6​	53.0​	60.0​	24.4​	21.2​
		6.9​	54.7​	60.0​	25.4​	22.9​	Average​
		​	Measured​	Achievable​	Required​	Calcul​	​
		Kitchen​	Temp​	Temp​	Output​	Output​	​
	kitchen​	LPM​	DegC​	DegC​	KW​	KW​	​
	10.90 - 57.5c	5.5​	57.3​	60.0​	20.4​	19.3​	​
	10.77 - 57c	5.6​	57​	60​	20.6​	19.4​	​
		5.5​	57.2​	60.0​	20.5​	19.4​	Average​
		Bath​	Measured​	Achievable​	Required​	Calcul​
		Tap​	Temp​	Temp​	Output​	Output​
	Bath tap​	LPM​	DegC​	DegC​	KW​	KW​
	6.11 - 53.7c​	9.82​	53.7​	50.8​	30.0​	32.0​	​
	7.67 - 48.4c​	7.82​	48.4​	62.0​	30.0​	22.6​	​
		8.82​	51.05​	55.7​	30.0​	27.3​	Average​
		Bath​	Measured​	Achievable​	Required​	Calcul​
	Retest​	Tap​	Temp​	Temp​	Output​	Output​
	bath tap​	LPM​	DegC​	DegC​	KW​	KW​
	6.45 48c​	9.30​	48​	53.2​	30.0​	26.6​	​
	6.36 48.5​	9.43​	48.5​	52.6​	30.0​	27.3​	​
	6.11 48.6c​	9.82​	48.5​	50.8​	30.0​	28.4​	​
		9.52​	48.3​	52.2​	30.0​	27.5​	Average​
		​	Measured​	Achievable​	Required​	Calcul​
		Shower​	Temp​	Temp​	Output​	Output​
Shower. SP 50C​	6.68 - 35c​	LPM​	DegC​	DegC​	KW​	KW​
Shower. SP 45C​	6.74 - 35.1c​	8.98​	35.0​	54.9​	30.0​	17.5​	​
Showr. SP 38C​	6.4 - 35.1c​	8.90​	35.1​	55.3​	30.0​	17.5​	​
		9.38​	35.1​	52.9​	30.0​	18.4​	​
		9.09​	35.07​	54.35​	30.00​	17.79​	Average​

 

[j3oeff]

With regards to previous flows,I have no idea why it is now slightly slower. I don't know if the engineer changed something or adjusted something. Like I mentioned above, I now have the noise inuse to have with the old boiler when switching hot water taps on which disappeared initially upon new install.

I've ran both hot water taps in the bathroom and the readings are below.

Gas start readings 456.977m3

Gas reading finish - 457.064m3

What am I looking for on gas bill usage btw?

 

[John.g]

Something like this, you might see about 5 lines down from the top left corner " consumption (110.9) M3 and energy used directly below it, (1257.3) kwh.

Presume below is a 2 Minute reading??
2 min gas readings, 457.064-456.977 = 0.087= 2.61M3/hr = 2.61*11.3 = 29.49Kwh. Boiler efficiency of 90% = 29.49*0.9 = 26.5kwh, short fall of 3.5kw so I suppose nearly there??.

The bath flow rate is IMO drastically reduced for whatever reason, if you were getting 14.5LPM at say a mains pressure of 4 bar, the pressure (mains or otherwise) is now only around 1.54 bar to give a flow rate of 9LPM.

 

[j3oeff]

Sorry yes,those are 2 minute tap runs.

I honestly don't know why the flow rate has dropped off, its only since the engineer visit.

Attached screenshots

 

[John.g]

Your gas usage was 152.1M3 which was converted to 1719.1Kwh = 11.302kwh/M3 which was the number I used in the calculations. (11.3)
If the engineer you are referring to was the Gas Engineer then he must have throttled the mains flow to the boiler, I don't think that's a good practice, the end user, IMO can do his own throttling at his own taps/shower etc, it may also play havoc with your shower mixer if the hot water pressure is now way lower than the cold pressure.
Can you do a quick check on your bath cold water flow, just the flow with the tap opened fully for say 2 minutes, this might tell you something.

 

[j3oeff]

Your gas usage was 152.1M3 which was converted to 1719.1Kwh = 11.302kwh/M3 which was the number I used in the calculations. (11.3)
If the engineer you are referring to was the Gas Engineer then he must have throttled the mains flow to the boiler, I don't think that's a good practice, the end user, IMO can do his own throttling at his own taps/shower etc, it may also play havoc with your shower mixer if the hot water pressure is now way lower than the cold pressure.
Can you do a quick check on your bath cold water flow, just the flow with the tap opened fully for say 2 minutes, this might tell you something.

Will do. I'm not measuring anything am I or looking for something?

 

[John.g]

If the hot & cold taps are the same size/type then one might expect the flowrates to be similar when fully opened so if you find the cold tap flowing 12 to 14 LPM (the hot is presently ~ 9LPM) then obvious throttling going on somewhere.
Some combi boilers have restrictors installed to limit the flowrate to give a dT of 35C through the boiler, a 30kw boiler will give a flowrate of 30*860/60/35,12.3LPM. with a temperature rise (dT) of 35C.