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And this was with the bath tap running just checking ?
Discuss New Boiler to replace a old Worcester 35CDi II in the Central Heating Forum area at PlumbersForums.net
No, kitchen one. Should it of been the bath tap? If so I'll do it in the morning nowAnd this was with the bath tap running just checking ?
Kitchen tap on full.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??
No, kitchen one. Should it of been the bath tap? If so I'll do it in the morning now
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.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.
Am I right in reading that as.... There is a fault with the boiler if those readings I give are correct?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
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. taIf you have 12 lpm coming out of the tap then yes
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
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?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)
Crikey, so some way off then on all of the upstairs outlets.You should be getting 12lpm and 30kw
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?
Understand the logic of getting the figures now, thanks.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.
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? TaYou 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'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.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
Fine for a shower but a bit cool for a bath as it will cool down from 43C fairly rapidly, throttling the hot tap to give say 9LPM should give a temp of 55C, add cold to give required bath temperature but I suppose that's what most people do anyway.Exactly your boiler should be at 30kw when doing 12lpm
Fine for a shower but a bit cool for a bath as it will cool down from 43C fairly rapidly, throttling the hot tap to give say 9LPM should give a temp of 55C, add cold to give required bath temperature but I suppose that's what most people do anyway.
Until the experts arrive,Given it was fine to this boiler being put in, would the boiler perhaps be limiting something or could if be a failed part etc.
So I have finally got onto Baxi and they are due to come out on Thursday, not ideal but hey ho. I have been on holiday all over xmas/new year so was unable to do anything. I had a shower last night and whilst it wasn't hot, it was enough to wash but definitely wasn't the 38C which the thermostatic tap was set at. I tried turning it to 50C to see if anything increased, it didn't in terms of hot, but went cold a few times, then back warm again. In the meantime, I emailed Baxi to ask the question re hot water and I got this response from their "technical team".
Good morning
Thank you for your email
The 830 has a 5KW less output to the Worecester 35CDii so that is where the issue lies.
The Baxi 836 Combi would have been the ideal replacement for it.
I will do my best. I have no issues with the boiler, it heats up the rads nice and toasty and is very efficient and quiet. They have sent this back this afternoon.Their reply wouldn't exactly fill one with confidence but at least they are following it up with a visit.
Make sure you emphasize that the boiler, isn't giving the required temperatures, more obvious at the lower flowrates.
If you assume cold mains now at 6C then any 30kw boiler should give a flow rate of 8LPM @ 60C, 8.5LPM @55C, 9.5LPM @ 50C, 11LPM @ 45C & 12.5LPM @ 40C.
If you want to, ensure DHW temp set to 60C and measure the mains temperature, the flow temperature and the flow rate (once again) from one of the Hot (only) taps that gives around 5 or 6 LPM, you can then show him/her up to date info which may convince them that you will be quite happy with a 30kw boiler once its fixed.
Hi John,This should be enough to demonstrate the boilers problems mainly at lower flow rates as, at the higher flow rates, your first two tests, the calculated boiler output is quite close to the rated boiler output of 30kw, but the last three clearly show a problem.
Mains Temp: 7.5C. DHW temp setpoint 60C, Boiler Rated Output 30kw.
3.74 secs @ 31.2c 16.04LPM 26.52kw Achievable Temp 34C Req output 30kw Actual output 26.5kw
3.86 secs @ 33.7c 15.54LPM 28.4kw Achievable Temp 35C Req output 30kw Actual output 28.4kw
6.30 secs @ 36c 9.52LPM 18.92kw Achievable Temp 53C Req output 30kw Actual output 18.9kw
10.16 secs @ 39.8c 5.91LPM 13.31kw Achievable Temp 60C Req output 21.6kw Actual output 13.3kw
16.26 secs @ 41c 3.69LPM 8.62kw Achievable Temp 60C Req output 13.5kw Actual output 8.6kw
Hi John,
Thanks for this and advising me what to say. I am going to carry out the above tests again this afternoon. Just to confirm, this is seeing how long each tap takes to fill a 1 litre jug and then what temp the filled jug is at?
Am I correct in saying the measuring of gas readings are 2 minute tap runs?
Set to 60c on boiler.Correct re jug, just rinse out a few times to ensure hot, also please take the mains cold water temp.
No need for gas meter readings.
Also ensure DHW temp setpoint set to 60C.
Mains Temp: 12.0C. DHW temp setpoint 60C, Boiler Rated Output 30kw. | ||||||
| | |||||
| Measured | Achievable | Required | Actual | | |
Kitchen Tap | 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 | | |
| | |||||
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 | | |
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 | ||
| ||||||
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 | ||
Bathroom | Measured | Achievable | Required | Actual | ||
Tap | Temp | Temp | Output | Output | ||
LPM | DegC | DegC | KW | KW | ||
14.6 | 35.0 | 41.5 | 30.0 | 23.4 | ||
14.1 | 34.9 | 42.6 | 30.0 | 22.4 |
Wow.....thanks for this John. It certainly makes it easier to understand what's going on now and cI an certainly put my point across to the engineer when he comes and even show him to experiment's I've conducted.Very similar to your previous readings, don't know what these two readings mean from the Bath Tap but not needed, the other two are fine.
19.5 - 41.2c
25.6 - 41.4c
I would also venture that the mains temp after a good run is ~ 7C so the actual output of the boiler with the bath flow rate of 14.6 LPM is more like 28kw but that doesn't in any way explain the problems at lower flow rates which will have to be addressed.
Mains Temp: 12.0C. DHW temp setpoint 60C, Boiler Rated Output 30kw. Measured Achievable Required Actual Kitchen Tap 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 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 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 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 Bathroom Measured Achievable Required Actual Tap Temp Temp Output Output LPM DegC DegC KW KW 14.6 35.0 41.5 30.0 23.4 14.1 34.9 42.6 30.0 22.4
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 |
Bathroom | Measured | Achievable | Required | Actual | |
Tap | Temp | Temp | Output | Output | |
LPM | DegC | DegC | KW | KW | |
14.6 | 35.0 | 41.5 | 30.0 | 23.4 | |
14.1 | 34.9 | 42.6 | 30.0 | 22.4 | |
14.3 | 35.0 | 42.1 | 30.0 | 22.9 | Average |
Perfect. You certainly can't get away from these facts and if he wants to conduct the same tests then he'll get the same results.A bit easier to see the problem all right, I have just cleaned it up a bit more here.
DHW Boiler MainsSetpoint 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 Bathroom Measured Achievable Required Actual Tap Temp Temp Output Output LPM DegC DegC KW KW 14.6 35.0 41.5 30.0 23.4 14.1 34.9 42.6 30.0 22.4 14.3 35.0 42.1 30.0 22.9 Average
These,These ones?,
Downstairs bathroom tap
6.23 - 37.7c
6.69 - 36.3c
Bathroom upstairs tap
5.96 - 35c
5:40 - 34.9c
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 |
Reply to New Boiler to replace a old Worcester 35CDi II in the Central Heating Forum area at PlumbersForums.net
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