New Boiler to replace a old Worcester 35CDi II

[j3oeff]

Oh Yes, quite right, corrected now and important to get it as your tests show, actually makes a better case as the average boiler output is lower again, at 21.1kw.
As a matter of interest, you seem to have shut the bath tap in a bit? to get the temperature up for the last two tests but the (flow) times make no sense, do you have them?.

Bath tap
4.12 - 31.7c
4.27 - 34.6c
19.5 - 41.2c
25.6 - 41.4c

	DHW​	Boiler​
Mains​	Setpoint​	Rated​				​
Temp​	Temp​	Output​				​
DegC​	DegC​	KW​				​
12​	60​	30​				​
​	Measured​	Achievable​	Required​	Actual​		​
Kitchen​	Temp​	Temp​	Output​	Output​		​
LPM​	DegC​	DegC​	KW​	KW​		​
5.6​	47​	60​	18.6​	13.6​		​
5.6​	43.5​	60​	18.8​	12.4​		​
5.7​	42.9​	60​	19.0​	12.3​		​
5.8​	42.3​	60​	19.4​	12.3​		​
5.7​	43.9​	60.0​	19.0​	12.6​	Average​	​
Downstairs​						​
Bathroom​	Measured​	Achievable​	Required​	Actual​		​
Tap​	Temp​	Temp​	Output​	Output​		​
LPM​	DegC​	DegC​	KW​	KW​		​
9.6​	37.7​	56.6​	30.0​	17.3​		​
9.0​	36.3​	59.9​	30.0​	15.2​		​
9.3​	37.0​	58.3​	30.0​	16.2​	Average​
Upstairs​						​
Bathroom​	Measured​	Achievable​	Required​	Actual​		​
Tap​	Temp​	Temp​	Output​	Output​		​
LPM​	DegC​	DegC​	KW​	KW​		​
10.1​	35.0​	54.7​	30.0​	16.2​
11.1​	34.9​	50.7​	30.0​	17.8​
10.6​	35.0​	52.7​	30.0​	17.0​	Average​
Ensuite​
Sink​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
9.0​	37.8​	59.8​	30.0​	16.2​
9.4​	39.3​	57.7​	30.0​	17.9​
9.2​	38.6​	58.7​	30.0​	17.1​	Average​
Bath​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
14.6​	31.7​	41.5​	30.0​	20.0​
14.1​	34.6​	42.6​	30.0​	22.2​
14.3​	33.2​	42.1​	30.0​	21.1​	Average​

19.5 - 41.2c
25.6 - 41.4c

I did turn the tap off abit too see if it got any hotter. I still followed the same process which was 1 litre jug fills which took as above....19.5 seconds and 25.6 seconds resulting in those water temperatures within the jug.

 

[John.g]

This is the icing on the cake j3, (I was looking for 20kw or something like that) as it proves beyond all doubt that when one tap is throttled in, the boiler only produces ~ 60% of the required output even though very well within its rated output.

	DHW​	Boiler​
Mains​	Setpoint​	Rated​			​
Temp​	Temp​	Output​			​
DegC​	DegC​	KW​			​
12​	60​	30​			​
​	Measured​	Achievable​	Required​	Actual​	​
Kitchen​	Temp​	Temp​	Output​	Output​	​
LPM​	DegC​	DegC​	KW​	KW​	​
5.6​	47​	60​	18.6​	13.6​	​
5.6​	43.5​	60​	18.8​	12.4​	​
5.7​	42.9​	60​	19.0​	12.3​	​
5.8​	42.3​	60​	19.4​	12.3​	​
5.7​	43.9​	60.0​	19.0​	12.6​	Average​
Downstairs​					​
Bathroom​	Measured​	Achievable​	Required​	Actual​	​
Tap​	Temp​	Temp​	Output​	Output​	​
LPM​	DegC​	DegC​	KW​	KW​	​
9.6​	37.7​	56.6​	30.0​	17.3​	​
9.0​	36.3​	59.9​	30.0​	15.2​	​
9.3​	37.0​	58.3​	30.0​	16.2​	Average​
Upstairs​					​
Bathroom​	Measured​	Achievable​	Required​	Actual​	​
Tap​	Temp​	Temp​	Output​	Output​	​
LPM​	DegC​	DegC​	KW​	KW​	​
10.1​	35.0​	54.7​	30.0​	16.2​
11.1​	34.9​	50.7​	30.0​	17.8​
10.6​	35.0​	52.7​	30.0​	17.0​	Average​
Ensuite​
Sink​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
9.0​	37.8​	59.8​	30.0​	16.2​
9.4​	39.3​	57.7​	30.0​	17.9​
9.2​	38.6​	58.7​	30.0​	17.1​	Average​
Bath​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
14.6​	31.7​	41.5​	30.0​	20.0​
14.1​	34.6​	42.6​	30.0​	22.2​	​
14.3​	33.2​	42.1​	30.0​	21.1​	Average​
Bath​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
3.08​	41.2​	60​	10.3​	6.3​	​
2.34​	41.4​	60​	7.8​	4.8​	​
2.71​	41.3​	60​	9.1​	5.5​	Average​

 

[j3oeff]

This is the icing on the cake j3, (I was looking for 20kw or something like that) as it proves beyond all doubt that when one tap is throttled in, the boiler only produces ~ 60% of the required output even though very well within its rated output.

	DHW​	Boiler​
Mains​	Setpoint​	Rated​			​
Temp​	Temp​	Output​			​
DegC​	DegC​	KW​			​
12​	60​	30​			​
​	Measured​	Achievable​	Required​	Actual​	​
Kitchen​	Temp​	Temp​	Output​	Output​	​
LPM​	DegC​	DegC​	KW​	KW​	​
5.6​	47​	60​	18.6​	13.6​	​
5.6​	43.5​	60​	18.8​	12.4​	​
5.7​	42.9​	60​	19.0​	12.3​	​
5.8​	42.3​	60​	19.4​	12.3​	​
5.7​	43.9​	60.0​	19.0​	12.6​	Average​
Downstairs​					​
Bathroom​	Measured​	Achievable​	Required​	Actual​	​
Tap​	Temp​	Temp​	Output​	Output​	​
LPM​	DegC​	DegC​	KW​	KW​	​
9.6​	37.7​	56.6​	30.0​	17.3​	​
9.0​	36.3​	59.9​	30.0​	15.2​	​
9.3​	37.0​	58.3​	30.0​	16.2​	Average​
Upstairs​					​
Bathroom​	Measured​	Achievable​	Required​	Actual​	​
Tap​	Temp​	Temp​	Output​	Output​	​
LPM​	DegC​	DegC​	KW​	KW​	​
10.1​	35.0​	54.7​	30.0​	16.2​
11.1​	34.9​	50.7​	30.0​	17.8​
10.6​	35.0​	52.7​	30.0​	17.0​	Average​
Ensuite​
Sink​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
9.0​	37.8​	59.8​	30.0​	16.2​
9.4​	39.3​	57.7​	30.0​	17.9​
9.2​	38.6​	58.7​	30.0​	17.1​	Average​
Bath​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
14.6​	31.7​	41.5​	30.0​	20.0​
14.1​	34.6​	42.6​	30.0​	22.2​	​
14.3​	33.2​	42.1​	30.0​	21.1​	Average​
Bath​	Measured​	Achievable​	Required​	Actual​
Tap​	Temp​	Temp​	Output​	Output​
LPM​	DegC​	DegC​	KW​	KW​
3.08​	41.2​	60​	10.3​	6.3​	​
2.34​	41.4​	60​	7.8​	4.8​	​
2.71​	41.3​	60​	9.1​	5.5​	Average​

Should be interesting to see what the engineer has to say tomorrow. I'll explain the situation and show him the info above. I'll let you know what has happened 👍

 

[j3oeff]

So, according to the Baxi Engineer, I have a faulty Thermistor. He didn't have one with him so is coming back on Friday to fit a new one.

 

[j3oeff]

Forgot to add, he didn't seem keen on listening to the outputs, etc. Asked me where I got all that from and asked if they are heating engineers or not. I'm glad he checked the kitchen tap though as that probably offers the best heat currently and even he didn't move his hand once with the hot tap running.

 

[John.g]

I suppose a experienced service guy doesn't need a flow cup and thermometer to tell him that a kitchen tap should be almost scalding hot, fortunate in a way that had the reduced output only showed up in the shower, I wonder how would he have diagnosed the reduced bath output of 21kw, his hand would scarcely have informed him that the flow temp was only 33C but should have been 42C. I hope new combi boilers with your problems are few and far between.

 

[j3oeff]

I hope so too. Hopefully, this is just an unfortunate one-off and once resolved I will have boiler-free troubles. I certainly did not envisage spending £1900 on a new boiler and 2/3 weeks later have an issue. Peace of mind is the 10-year warranty I guess!

 

[j3oeff]

Genuinely think my old broken boiler worked better than this one haha. Turned heating on around 4.30pm via hive from work and just got home to this.

 

[ShaunCorbs]

Pressure is down need to fill the system

 

[j3oeff]

Pressure is down need to fill the system

Yes I managed to find out what it was on Google. Is that normal though? Pressure to drop below 1bar from a new installation on Xmas Eve? Or could it be down to the 2 faulty radiator valves I have? Maybe letting small amounts of air out?

 

[ShaunCorbs]

Might be just all the air has settled and you haven’t seen the pressure is slightly low happens winthin a month of a new boiler / system as there’s a bit of air trapped etc

 

[John.g]

Tomorrow is D day, hopefully you will then be be luxuriating in a bath of HOT water with a bottle or two of champagne.

 

[j3oeff]

Tomorrow is D day, hopefully you will then be be luxuriating in a bath of HOT water with a bottle or two of champagne.

No champagne here my friend. We are expecting our first child so the wife can't drink and doesn't approve if I do without her haha.

Anyway, we have hot water 😬

Few 1l approx fills runs and timings.

Bath sink
7.12 - 52.4c
6.98 - 54.7c

Bath tap
6.11 - 53.7c
7.67 - 48.4c

Ensuite
8.39 - 56.4c
9.10 - 53c

I certainly cannot hold my hand under any of the hot water taps for long now.

 

[ShaunCorbs]

Looks much better 👍

What did he do ?

 

[John.g]

Can you measure the mains temp please.

 

[j3oeff]

Looks much better 👍

What did he do ?

Replaced a faulty thermistor

 

[j3oeff]

Can you measure the mains temp please.

Kitchen one?

 

[John.g]

Anywhere that's representative of the cold mains entering the boiler so cold kitchen tap should be OK after a few minutes run. You might also take two readings from the hot kitchen tap as that was very poor before.

 

[John.g]

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​

 

[j3oeff]

Cold tap in kitchen is 7c and filled in 10.04

Hot tap kitchen

10.90 - 57.5c
10.77 - 57c

I've just had a shower and the thermostat tap was set to 50c but it was no way that. I think I may have a broken valve or something. How would I be able to find out?

 

[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?