Baxi at constant low rate

[essexsi]

Hi

I have just spoken to the RGI that I go out with to build my experience. We serviced a Baxi Bermuda BBU on friday and the customer has called him back. When lighting the boiler pilot the burner lights at a low rate. When the boiler temp is set to 0 the burner is still at a low rate and not just the pilot alight.

I thought that the thermoelectric valve may be letting by, but this was rock solid on TT.

As a beginner this has me stumped , you chaps have any ideas?

cheers si

 

[baxpoti]

First thing that comes to mind is the gas valve is letting by.

What model of BBU is it?

 

[Agile]

If the RGI you go with did not treat this very seriously then he is not a good person for you to be learning from!

Its not immediately obvious what has happened but it seems the gas valve is somehow letting by. Perhaps some dirt got into it?

Did he completely remove the burner part and carefully clean the lint trap box?

Tony

 

[essexsi]

thanks for the reply

its a 552

tested the FSD by isolating gas and it operated in 34 secs. Then restablished gas and TT for 2 mins at 21mbar and rock soild, so I believe the gas valve is not letting by.

thanks si

 

[namsag]

Check the gas valve is not getting voltage to it if there is none it is an intermittent sticking of the valve which is not unusual but is immediately dangerous

 

[HarrogateGas]

thanks for the reply

its a 552

tested the FSD by isolating gas and it operated in 34 secs. Then restablished gas and TT for 2 mins at 21mbar and rock soild, so I believe the gas valve is not letting by.

thanks si

If this is the case you definatly need a knew teacher..........testing at 21mbar will not pass you our acs!

 

[essexsi]

thanks for the reply Agile.

He did take it very seriously and I believe is round at the place now. I was just inquiring as to what could be the different possibilities for my own development.

As I say we TT the gas valve and it was rock solid when we left. The burner was taken out and cleaned, as was the lint filter.

thanks

 

[Agile]

Unfortunately that demonstrates your lack of understanding of how the gas valve works.

Many RGIs dont understand either and many teachers have the same problem so its a regenerating lack of knowledge!

Perhaps I can explain although I sometimes wonder why I should spend so much time helping others free!

The gas valve has two sealing parts which are in series with each other. The first is opened when you push the knob. If the voltage from the thermocouple is present that part will stay locked in the open state.

The pilot light is supplied from just after the first seal which is now open and the pilot stays on.

The second seal is opened when the electricial supply is applied to the gas valve solenoid. Its that SECOND seal which is letting by.

Its probably a little dirt on the seating and rapidly pulsing power to the solenoid with the boiler on might clear it otherwise it needs a new valve.

Tony

 

[essexsi]

my apologies harrogate gas, as soon as I hit submit I thought "you idiot". Trying to type too fast.

 

[essexsi]

Thanks for your time and trouble Agile. I and many others on here appreciate the posts of you and the other more experienced RGI's .

So when you isolate the gas and the FFD operates, am I correct that a TT done then will only prove the tightness of the 1st solenoid and not of the second main solenoid?

many thanks si

 

[Agile]

Exactly! But dont call it a solenoid as you are not testing a solenoid! You are testing the effectiveness of the gas valve seal.

If you wanted to do a tightness test on the SECOND seal then you would seal the pilot jet gas outlet and hold the knob down in the pilot restablish mode.

The complaint about you doing the tightness test at 21 mB was only on a technical point that the nominal pressure for a tightness test is 20 mB not 21 mB.

In reality it would make no difference to do the test at any pressure over 20 mB if you are only testing the gas valve.

For normal tightness testing you should not do it over 20 mB in case the regulator locks up as that would hide any leakage between the reg and the EC.

Tony

 

[essexsi]

Tony thank you for your reply. In this situation then it is ID as a gas valve is letting by. If you then do a TT on primary gas valve and do not understand how the gas valve works then this test proves nothing. well only that the primary gas valve is not letting by.

It really is true that ACS does not teach you how to be a gas man.

Thank you all for your replies.

 

[essexsi]

hi chaps

As way of an update I went with the RGI to change the gas valve. It is the first one that I have done and found it quite challenging. Good job I was being coached through it !

I know for you guys its a simple job, but as a newbie I found it a good learning experience. Once in place I tightness tested, set the burner pressure and took a gas rate, everything spot on.

Thanks all for your posts

all the best si

 

[Agile]

There is not much more simple that a gas valve on a 552 !

But you have to start somewhere and its best to start with a simple one.

Try a gas valve on an Ideal Minimiser with no right hand side access, thats more chalenging!

The important thing to know is that you dont just change the gas valve. You have to set it up for min and max gas pressures when its a modulating valve. Some later boilers dont make it very easy to do that.

Tony

 

[essexsi]

hi tony thanks for your input throughout.

You are right that we all have to start somewhere and I am definatley at the bottom!

I made sure that the gas valve was set up correctly before we left the job. I want to make sure that everything I do is by the book. I believe that if you are going to do something you should do it right and not cut corners.

I'll be the first to admit that I have much to learn, not only about the gas side, that I would like to specialise in,but also the water side which I appreciate I need to know alot more about if I want to service and repair boilers.

With a view to this I am thinking of approaching more RGIs about work experience, so to all viewing if you get a letter or call from a Simon near Southend in Essex then please be sympathetic!!

thanks again si