Vaillant 937 plus Hot water flow

[gas4you]

When working on full power this will use a minimum of 4m3/hr gas.

As said before you can't take a reading of the burner pressure on these, it has to be set up with an FGA.

Your supposed corgi has not installed/commissioned this boiler correctly. Whether this is the cause of such bad HW performance or not is questionable, but without the boiler running to manufacturers specs you will never know where to look for the problem

 

[Agile]

In that case the CORGI probably did measure the gas rate.

However with a restricted flow rate the boiler will modulate down and consume less gas!

I would guess with the full spec flow rate it will consume the correct amount of gas as designed.

Tony

 

[gas4you]

One can only assume that IF the installer is a genuine RGI who is familiar with this boiler, he would have set the boiler to max fire rate to gas rate it and set the co2 correctly, wouldn't he?

A lesser flow rate would then not ever come into the equation

 

[Agile]

Whats the chance he used an FGA ?

Setting it to max fire rate with a low flow rate would cause it to overheat pretty quickly! Presumably it just cuts the flame if it gets too hot?

In any case his recorded value of 3.60m³/h means he would not have done that.

Smurf, did he use a complicated looking instrument with a digital display with black tubes going to the top of the boiler?

Tony

 

[smurfy125]

Yes you mean a flue gas analyser. Yes he did and got a CO2 reading of 9.1%. I watched him do it and have a receipt of the test. The cold water flow that i measured giving 22-23 li/min was taken from the bath tap. The bathroom 22mm pipe is taken via a tee from the 22mm pipe that is feeding the boiler in the loft, so it goes from the main to the boiler and has one tee joint in the pipe suppling the bathroom.
Thank
All

 

[smurfy125]

The corgi guy i know is genuine because i went through the corgi site to find him and is local to me. He did say that he only fits and deals with Worchester bosch.

 

[fitz1]

check the inlet filter

 

[simond]

I suspect a poor working pressure on the water main is the problem here.

Proper installers (such as most on here) measure the flow rate and pressure before specifying a combi boiler.

Can you confirm what is the standing pressure of your water main? If it is low the flow rate through the relatively complex passages in a boiler will be reduced compared to an open tap. Which seems to be what you are reporting.

This preoccupation with gas is a red herring, for the second time.

 

[Agile]

I measure the dynamic pressure as thats the only way to get a meaningful idea of the pressure/flow rate.

Typically I measure the flow rate obtained whilst leaving a pressure of say 0.5 Bar in the supply pipes.

Just measuring the open pipe flow rate leaves you unable to accurately guess the actual flow rate that you will obtain through a combi into a shower.

Very typically the dynamic flow rate might be HALF of the open pipe flow rate but that can vary according to the mains pressure and the supply pipe resistances.

Tony

 

[smurfy125]

I called vaillant today and they said it sounded like a problem with the shift storage tank, but they are coming out on thursday to have a look. So i will let you all know what they say. In the mean time if anyone has anymore ideas then please let me know
Cheers

 

[Agile]

Perhaps Dave knows better but I dont see that as being the problem.

However, it may help you with them saying that because if its just poor mains flow/pressure then it might become a chargeable visit if called under the warrrantee. As they thought it was something else then you should not get charged.

Tony

 

[smurfy125]

Had vaillant guy out today who said he found dirt in the filter and removed the restrictor and said that i am getting 14-15 l/min. He also check the incoming water pressure which is 2.5bar. When i asked him why i was not getting the 20 l/min out of it he said it was because of my water pressure. Is 2.5bar not enough then? After he had gone i tested the water again and seems to be about 14 l/min so a bit better but even with the charged tanks on it still gives the same so i think something is still wrong somewhere.

 

[kaboom]

abc

 

[Agile]

The static pressure is irrelevant.

Your supply pipe has considerable resistance and with the boiler as well you will be getting less.

Very understanding boiler engineer there from Vaillant.

Your installer was not so helpful!

Tony

 

[vaillantassisstancefroman]

I agree with Simon. I have had a 937 now for 4 years and it has always performed badly. I have had vaillant out a number of times and a number of plumbers look at it. Until last week I was given every reason under the sun as to why it was not working - gas pressure, pipe size in the house etc etc. I had a new gas main fitted with bigger pipes and this made no difference. For everyones benefit i thought i would set out the problem, how I proved this was the problem and the likely solution (note this is not yet fixed but should be soon).
1) The problem - house is luke warm in winter not hot and water flow to hot taps is poor. Also if you turn 2 hot taps on then 1 goes cold (the 937 should allow 2 or 3 hot taps on at a time).
2) Identifying the problem - we measured the cold water flow from the water main with a funnel device (I think it is called a Weir gauge). This measured in excess of 25 litres per minute. Then we cut the hot water pipe just below the boiler and measured the water flow. It gave 12 litres per minute. This proves that it is the boiler and nothing else giving the problem. You can even do this with the boiler turned off and will see a significant reduction in water flow once water has passed through the boiler. (someone in one of these threads suggested that this shows a a significant water leak - this is nonesense as I have seen the measurements myself).
3) The (likely) solution - there is a water filter and a water flow restrictor at the end of the pipe where the cold water main enters the boiler. One of these is either faulty or blocked. We will have them both replaced and repeat the test.
Please note I am not a plumber but have had to become an expert in this as very few people seem to know about this issue.
I hope this helps others as this has been a big problem for me for many years now. Vaillant guys do not seem aware of this potential issue.