Vaillant 937 plus Hot water flow

[smurfy125]

Hello All, i need some advice.

I have just installed a vaillant 937 plus boiler in the loft and just had it commissioned. I am concerned as to the amount of hot water i am getting out of it, because it seems to be poor. When i turn the tap on for the sink in the bathroom the pressure appears to be ok but when the bath tap is turned on, the flow and pressure is rubbish. I expect the pressure to be less but the flow i thought would be good because the pipe is 22mm. The flow of cold water to the boiler is 22-23 litres per minute and the hot water output seems to be about 11 litres per minute. The boiler should deliver up to 20 litres per minute with the aid of the storage tanks or 15 litres per minute if these have been discharged. The water pipe to the boiler is in 22mm then reduces to 15mm to go into the boiler and again the same with the hot water pipe coming from the boiler is in 15mm going to 22 mm. Can anyone shed any light.
Thanks.

 

[fitz1]

what length and size is the gas pipe.

 

[smurfy125]

The run is about 10 meters and the sizo of the pipe is 28mm.

 

[fitz1]

are there any inlet filters and is the burner pressure correct.(gas rate)

 

[smurfy125]

The gas burner pressure was checked by the corgi guy who commisioned the boiler and told me it was correct. There are no inlet filters that have been installed.

 

[fitz1]

what flow rate has the engineer wrote on the commissioning log book.

 

[smurfy125]

i will have to let you know tonight fitz1 because i am not at home until tonight and i dont have the paperwork on me, so i will post you that information later.
Thanks

 

[fitz1]

there is an inbuilt filter on the cold water inlet.

 

[gas4you]

You can't test the burner pressure on these, just the gas inlet pressure, which as long as you have 17mbar at the gas valve you will have 20mBar at the gas pipe inlet to the boiler.

These have to be set up for 9% CO2 with an FGA.

 

[smurfy125]

Yeah the gas pressure was checked and im almost sure this was at least 18 mbar but again i will check the paperwork and post all the information tonight.

 

[ChrisR]

When i turn the tap on for the sink in the bathroom the pressure appears to be ok

Measure the flow, in litres/minute

but when the bath tap is turned on, the flow and pressure is rubbish.

Measure the flow, in litres/minute

Then turn them both on together,
Measure the flows, in litres/minute

COuld be a faulty tap, your perception, neither, or both

While both taps are on full, check the gas usage rate at the meter. It explains how to, in the FAQ section.
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what flow rate has the engineer wrote on the commissioning log book.

I bet "when he measured it" it was exactly the same as the figure in the front of the book.
Just like all mine

 

[Agile]

Hello All, i need some advice.

The flow of cold water to the boiler is 22-23 litres per minute and the hot water output seems to be about 11 litres per minute.

Can anyone shed any light.

Thanks.

If you really had 22 li/min going in and only 11 li/min coming out then the boiler would be leaking 11 li/m !

Of course that is not happening so do the checks that Chris asked and we will see what we can suggest.

I suggest that the 22 li/m was measured as "open pipe" rather than dynamic and the reduction with the boiler connected is just as a result of the resistance within the boiler.

Unless the distribution within the house is particularly long then the output hot water pipework should be in 15 mm and best insulated.

Even if it is long then I would be fitting seperate 15 mm feeds from the boiler to different outlets as this reduces waiting time and wasted gas comsumption.

Tony

 

[smurfy125]

Had a look at the benchmark paperwork and the gas rate was recorded as 3.60 m3/hr and gave a maximum burner operating pressure as 19 mbar. I also measured the li/min that was coming from the sink and this was exactly the same as the bath (11 li/min) exept gave the perception as more because the pressure was better because of the 15mm pipe feeding it. I worked out how much gas i was using from the link that was supplied and i worked it out to be 38.19kw because i have a metric meter and timed it for 2 minutes which gave me 0.119 which i then multiplied by 321.

 

[Agile]

Nupty CORGI then?

Gas consumption of 3.60 m³/h sounds like exactly what the book will say !

And the burner pressure is definately NOT 19 mB.

19 mB sounds like the WP at the boiler inlet ( but did he really measure that on full power ?

Tony

 

[simond]

What has gas pressure got to do with this?

The OP is saying he is only getting 11l/m out of the boiler. I assume he would get the same with NO GAS AT ALL.

Clearly there is a restriction on the water side, or the incoming flow/pressure is unsatisfactory. Why are you fannying around suggesting measuring gas rates?