Problems with new central heating system

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packetvoodoo

Interesting problem for you good chaps to get your teeth into...

System (converted from open to sealed system with following):
New Vaillant 630 system boiler. Pump integrated into boiler.
New hot water cylinder in airing cupboard.
New Honeywell 3-way valve
New ST6400 programmer
Old header tank removed.
All pipework in airing cupboard replaced.
Only old stuff remaining is the underfloor pipes and radiators.

The problem...replicated by:
1. Bleed the system using P0 program (run 3 times). bubble-free in both heating and hot water circuits. Bled system pressure ~1.1bar.
2. Run the hot water. Heats up. No bubbling noises. Heat until temp sensor on cylinder turns off. Shut off hot water demand on programmer.
3. Run the heating. All fine. Heats up. No bubbling noises. Pressure ~ 2.3bar at 75degres C.
4. Turn off the heating. Assume 3-way valve puts output back to B only to run off excess heat through the cylinder. This is where things go wrong - can hear LOTS of VERY LOUD rumblings and bubbling suddenly. Sounds like it's sucking in large quantities of air, but that's not possible with pressure at >1bar, right?

The system isn't leaking - pressure stays constant over period of days, and no signs of any water leakage.

The fitting company have been back to replace the cylinder thinking that the heating coil was ruptured, but this hasn't fixed the problem. I'm getting them back hopefully this week.


Grateful for any thoughts as to potential faults from you good folks,
PacketVoodoo
 
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With a pressure of 2.3Bar on heating only sounds like the system is too big for the in-built expansion vessel. May need an additional expansion vessel.

Has the installer adjusted the in-built by-pass as per the Instructions?

The pump can be adjusted to suit the heating load - has this been done?
 
P

packetvoodoo

giblets - thanks for your reply.

I'm not sure what your comment about the expansion vessel means - surely big enough if came integral to the boiler?

Tried range-rating the boiler output down to 20Kw, no effect.

Don't know about the by-pass - will check when installer comes back.

The AAV on the pump is fully open.

Pump has been turned down - no effect.



Thanks,
PacketVoodoo
 
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surely big enough if came integral to the boiler

Not so. It depends on the installed volume of the system. The internal exp vessel will only cater for a specific system volume. Anything larger may need an additional vessel.

How has the pump been turned down?
 
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packetvoodoo

Thanks for the tip re expansion vessel - will discuss with installer. Pressure seems to be ~1.5bar at 33degrees C in the expansion vessel. Read elsewhere that this should be 0.75bar at cold - will check again when cold. Could too high a pressure in the expansion problem cause the problems indicated?

As for the system volume - difficult to say - but two floor largish 4 bed house with 13 radiators. Downstairs radiators are drop fed from first floor. The boiler is allegedly oversized for the property if that helps (30KW).

Pump was reduced using the boiler advanced settings - choice of 1 and 2 speed IIRC.


Your continued help is much appreciated.

Thanks,
PacketVoodoo
 
P

packetvoodoo

Clarification. Bled system pressure was 1.1bar at the first floor (next to the cylinder). Actually 1.4bar on the boiler.

All other pressure readings are at the boiler on the digital display.


Thanks,
PacketVoodoo
 
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No not the AAV, the ABV to the bottom left of the pump in the boiler. This has to be adjusted with a flat blade screwdriver. They have been known to stick shut due to the system being cleaned too well and the chemical cleanser removing a layer off the metal valve.

Are there any fault codes appearing?

As a side issue I would run this boiler at 65C, not 75C, to help it condense better.

I always leave my Vaillants set at 65C with a HW cylinder and 60C on a combi, unless WC has been fitted.
 
P

packetvoodoo

ABV - another chat to have with the installer.

No fault codes, no.

I'll turn the temp down to 65C as you suggest.


Thanks,
PacketVoodoo
 
P

packetvoodoo

Reading back through this thread, I realise that I've mislead you a bit javascript:emoticon(':oops:') - part 4 of the original post was before the replacement cylinder was fitted. Best to start again.


The problem...methodically replicated by:

1. Fill up system from empty. Bleed the system using P0 program (run 3 times) and bleed radiators. Sounds bubble-free in both heating and hot water circuits. Bled system pressure ~1.4bar.

2. Run the hot water side only. Heats up. No bubbling noises. Heat until temp sensor on cylinder turns off (60 degrees C). Pressure ~ 1.9 bar at maximum temp. Shut off hot water demand on programmer. All good so far.

3. Run the heating only. 3-way valve moves to heating only. All fine. Heats up. No bubbling noises. Pressure ~ 2.3bar at 75 degrees C. Still good.

4. Shut off all heating controls, 3-way valve moves to HW-only to run off excess heat from the boiler. No problems. Pump overrun runs for ~ 5 minutes. Still good.

5. Turn the hot water back on. Change cylinder thermostat to 80 degrees C to ensure demand for hot water. Still good.

6. Turn heating back on. Both heating and hot water are now running at same time. Set thermostat to 30 degrees C to ensure demand for heating. Still good.

7. Confirm that both work as expected. Pressure is ~ 2.3 bar at 75 degrees C. No air noise / bubbling. Still good.

9. Here's the crucial bit -- Turn off heating demand. This is where the problems start...

10. 3-way valve moves back to HW only (confirmed). Can hear LOTS of VERY LOUD rumblings and bubbling suddenly. Sounds like large quantities of air are in the system. Noise doesn't seem to be lessening - sounds like a continuous supply of air being added.

The system isn't leaking - pressure stays constant over period of days, and no signs of any water leakage.

The scenario is completely repeatable. Running hot water and heating independently works absolutely fine.


Had the installer back yesterday. He fitted another AAV on the flow side of the cylinder pipework (just after the three-way valve). Seems to have made no difference as yet.

He dismissed your advice regarding the expansion vessel and ABV without even checking anything. He suggests that 2.3 - 2.4 bar at 75 degrees C was fine.

Advise elsewhere in this forum suggests that as long as the system pressure never drops below 1 bar, air cannot get in. Is this correct? The system pressure -never- gets anywhere near 1 bar (minimum 1.4 bar cold).

He's suggesting that these systems need up to six months to settle down, and I'm over-reacting...the fact that the noise is so loud that you can hear it all over the house doesn't seem to concern him.

His next suggestion is to replace all of the underfloor pipework...


Appreciate your thoughts,
PacketVoodoo
 
P

packetvoodoo

Sorry, replying to own post.

Key question I guess is what actually is the difference between (2) and (10) in the list, apart from 0.5 bar of pressure? Why would (2) be fine yet (10) cause problems? System pressure for (10) isn't any greater than (3).

Confused!


Thanks,
PacketVoodoo
 
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Sounds like the Bypass is shut or not open enough for the pump over-run to circulate the water for a couple of minutes. If the MV shuts then the pump needs to get rid of the excess heat in the boiler so runs the pump, if the water cannot circulate to somewhere it will make strange noises.
Should this system have its own auto bypass aswell as the one on the boiler? I am not famillure with this type of boiler but I'm sure G4You will let us know.
 
P

packetvoodoo

If I've understood your posting correctly cozzmic...

The system isn't in run-on mode when the problem occurs. HW on (5) + heating on (6) + heating off (9) = HW only mode.

Run on mode would be (4).


Thanks,
PacketVoodoo

EDIT: All boiler settings are at their defaults, with the exception of the pump (D.19) which is set to 1 (pump speed always at speed 1) rather than the default 2. Boiler is NOT range rated. Flow and return temperatures measured by the installer (on the commissioning sheet) were 69 and 58 degrees C respectively, though pump speed was 2 when this was measured.
 

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