Combi boiler hot water prob

[fire boy]

Hi to all
Noob to the forum

Can anyone advise me on my boiler

I have a valiant combi boiler (about 9 years old) fitted in my ex council property.

When running the hot water the boiler fires up for a few seconds and then cuts out.

Central heating works fine., but the boiler sounds noisey when running the hot tap(water cavitating??) along with a hissing noise which gets louder until ithe flame cuts out.

I know the diverter valve was replaced about two years ago.

I also know that I can't fix it myself but some idea to the problem and the cost involved will ease my mind.

Kind regards Brian

 

[meldrew's_mate]

Assume you have a Vaillant boiler.

At that age it could be a VUW variant, so a model no. would help.
The VUW (VCW?) has a "water section" at the front often erroneously referred to as the diverter valve, the diverter valve proper is on the rhs and has switches attached. So please confirm which bit was replaced?

What's the system pressure?
Does the flame first go high, then drop to a low flame b4 extinguishing?

 

[fire boy]

Yes it's a Valliant boiler

I can't seem to find the model number though.

If it helps on the lower part of the boiler ther is a hinged flap with the controls behind.
ther is a row of lights on the left with a green on/off dial below and next to that a further 3 green dials.
1 for h/w
1 for c/h
and one to select hot water heating or both.

The system pressure is about 2.5 bar on the gauge.

Looking at the flame with hot tap running it seems to shrink in size just B4 it clicks out.

The valve that was replaced is just behind the pump.

I remember when the guy replaced it he left a tap closed and when it got cold the c/h failed to work but the pump became VERY hot.

I found that fault myself but could this new fault be pump failiure?

 

[kevplumb]

turbomax

 

[fire boy]

Thats the one

 

[kevplumb]

hope not
it's in my kitchen

The system pressure is about 2.5 bar on the gauge.

far toooooo high
should be 1.2 COLD

problem could well be diverter valve the early ones liked a diaphram or two

and where known to snap the arm on the microswitch

 

[fire boy]

Boom Boom

+++++++++++++++++++++++++++++++++++++++++++

Can I do this myself?
After all I do repair fire engines for a living
+++++++++++++++++++++++++++++++++++++++++++
Can I drop the pressure by the bleed vent?

Also can I replace the diphragm or a whole new valve?

MOD

please use the edit button

 

[kevplumb]

dont see why not

if you have the installation and servicing instructions it helps

 

[fire boy]

I've now got to go to stoke newington to fix a fire engine with no siren ah the joys of callout
Any help would be great

 

[kevplumb]

only docs ive got are spares list if its any good to you e mail me (adress in profile)

 

[fire boy]

someone suggested that I remove the secondry heat exchanger and flush it through with descaler.........which i did and hey presto!!

It worked

A big thankyou to all that posted on this thread

especially to Kevplumb