Will an 8 Ltr expansion vessel do (with video)

[kevoffthetee]

I'm just wondering in an 8 Ltr external expansion vessel would be up to the job if the original expansion vessel was isolated.

As per my other post, After a heating engineer installed the external expansion vessel and pump i get a huge gurgling noise every so often where the pressure bounces and the burner cuts out. The heating and water works fine for hours but every so often when the burner kicks in I get the problem

I had the engineer out today around 3 and he said that he had mistakenly left the bleed screw on the pump slightly open and that it was just air in the system. He got the air out of the system and left after explaining all to my wife.

It was fine until 9 o clock and when it fired up the problem came back. I turned the boiler off and then back on again but this time put my hand on the original EV which was the root of the gargling noise.

Can this be isolated from the system, at least to remove this from my list of possible causes as I'm doing my head in and ready to throttle him.

If I were to drain the system can I isolate this myself or is it a no-go

http://youtu.be/I-FjjUWthzQ

 

[kevoffthetee]

Sorry, it's a chaffoteaux britony combi 80 running 5 rads and a towel radiator

 

[Nige F]

It might be that the vessel is fitted upside down - looks like the tapping is @ the top ... probably not - you said the noise was from the original EV

 

[ianmcd]

Its hard to tell with that video but it sounds as if as soon as the burner stops then the pump stops at the same time ? the pump should run for a short time after the burner goes out (demand ceases) to cool the boiler ,it sounds like this isnt happening

 

[kevoffthetee]

Hi guys, thanks for the replies

The engineer was due our today but claims to have an upset stomach and will be here tomorrow

Ian- I believe the pump and burner switch off simultaneously after the pressure bounces all over the place and the gurgling noise. After a few minutes, the boiler starts up again and then the sequence repeats

 

[hazetimesfive]

yes the caviar and fois gras plays havoc with ones digestion

 

[ianmcd]

Hi guys, thanks for the replies

The engineer was due our today but claims to have an upset stomach and will be here tomorrow

Ian- I believe the pump and burner switch off simultaneously after the pressure bounces all over the place and the gurgling noise. After a few minutes, the boiler starts up again and then the sequence repeats

Well thats your problem , when the burner and pump switch off at the same time the heat in your boiler causes the water to boil which is causing the noises, the pump over runs to cool the system water and stops once the heat exchanger is cooled sufficiently

 

[ianmcd]

CENTRAL HEATING MODE
With a demand for heating the pump (11) circulates water
through the primary circuit. At a flow rate of approximately
250 I/hr the central heating flow switch (9) operates,
commencing the ignition sequence.
The main burner (6) ignites at 1/3 rate then switches to full
gas rate. The gas valve (7) controls the gas rate “HIGH -
LOW” to maintain the heating temperature measured by the
thermostat sensor (16).
When demand is satisfied the burner is extinguished, the
pump continues to run. The duration of each OFF cycle is 3
minutes before re-lighting automatically. Each ON cycle
commences with a 45 second duration at third gas rate
before switching to full rate if necessary.
On completion of a heating period the pump will continue to
run for a period of 3 minutes (PUMP OVERRUN).



That is a quote from page 6 of the Baxi genesis operating instructions the C&M that you have is the same boiler

 

[kevoffthetee]

The burner and pump only cut out is the result of the pressure fluctuation and gargling noise from the expansion vessel. This intermittantly happens as the boiler fires up, but not as its cutting out.

Yesterday boiler ran fine all day but at 9pm as the timer kicked in the pressure and noise issue started again

 

[ianmcd]

It could possibly be a fault with the primary flow switch they are prone to dropping out, the DHW and the CH are interchangeable but the primary one uses a soft spring so try swapping them over and see if this helps but remember to swap the spring over you will see what I mean when you take it out

 

[kevoffthetee]

I've decided to fault find myself and wondered if it could be the 3 way diverter

Please read - //www.diynot.com/forums/plumbing/can-a-3-way-valve-be-stuck-in-neutral.353393/

 

[ianmcd]

well really glad you have decided to fault find your self, your boiler in the video is overheating because the pump is stopping at the same time that the burner stops it has absolutely nothing to do with the old expansion vessel still being connected or the new expansion vessel being the wrong size (which it is not ) the boiler you have was very poor when in production and not a lot left in service but good luck in your fault finding

 

[kevoffthetee]

Thanks Ian

What could cause the pump to cut out at the same time? If the pcb, it only had a new pcb at xmas due to the boiler not firing the 2/3 burner

 

[ianmcd]

Been a while Kev since I worked for C&M at the time I knew the boilers inside out but we are going back about 15 years and as said the boilers were poor then, the flow switch was a known problem as was the diverter valve but yours is definately a problem that the pump over run is not in operation, this could happen with either of these faults, to prove my theory put a 240v AC supply direct to the pump (isolate the designated supply obvioslly) and I guarentee this symptom will not happen as the heat will be dispersed as already said it is not an expansion vessel problem

 

[kevoffthetee]

I know what your talking about with the over run on the pump (running after the burner has cut off), but would the over run cause the pressure to rise as the burners are running and then the boiler to cut out in the first place, or be a cause of the resulting noise after the cutout.

I might have misunderstood or got the series of events in the wrong order

The fan starts, the pump runs, the burners fire, the pressure rises causing the boiler to cut out and stops the burners and pump then leading to the gurgling noise.

Thanks again Ian, its much appreciated