Vaillant ThermoCompact won't start after system refil

[raycampion]

I'm not sure the exact model (was in the house I moved into)- but the book says VU 142/1 E, 182/1 E, 242/1 E, 282/1 E

Recently I drained the system to add two new radiators. When finished I refilled the system, but when I try to start the boiler, it won't start. When the power is turned on, the Demand indicator lights up, then a few seconds later the fan starts and the fan light comes on, followed by the ignition indicator. The system stays like this for a few seconds before the fan turns off, and the only lights that are showing are the demand light which is permanently on, and the power indicator which flashes on and off. Have bled the air from around the pump, and the container at the top of the boiler unit.

I wasn't left the commissioning manual, and their website doesn't have it as a download. Would greatly appreciate if anyone has any idea on what is going on. My guess is that it's an airlock somewhere, but I can't find another drain valve.

Tks Ray

 

[Agile]

It sounds as if its just some air in the system causing the flow switch to fail.

Behind the pump is the AAV and the cap on that should be just loose to enable air to be expelled.

I do hope the thing at the top was not the expansion vessel !!! Hopefully it did not have a Schraeder valve like your car tyres?

Tony

 

[raycampion]

Hi Tony,

I've loosened the cap and it didn't have any affect. On the thing at the top - it did have a car valve type valve which I depressed until no more hissing sounded - have I messed it up?

Tks for the help
Ray

 

[markplumb]

sounds like you've released the pressure from the expansion vessel

 

[raycampion]

Ah - I see. Is there anything I can do, or do I have to get a pro in to sort it out. As I drained it, I did notice that there was a drop in the system pressure

Cheers
Ray

 

[Gasguru]

Yes.

The vessel at the back is supposeed to contain air.

Drop the system pressure down to zero and pump up the vessel to aboiut 0.8 Bar.

Make sure the system pressure is at zero on the gauge with 0.8 Bar in the vessel.

You may have a blocked auto air vent. If there is air trapped in the boiler the flow switch located just above the pump will not operate and allow the boiler to fire up.

 

[Agile]

Yes, you have !!!

But its not that which has stopped the boiler firing!

Follow the FAQ to repressurise with a footpump after letting ALL the pressure out of the system and LEAVING the system open until you have about 0.9 Bar in the EX vessel.

The boiler has probably just got air in it. The AAV may well be blocked and not collecting and expelling. Leaving it for a while may still be allow some air to come out.

Tony

 

[raycampion]

Thanks - will give that a go now. The boiler was working just before we drained the system, and didn't work again after refilling, so I'm guessing it's probably not a block - just an air lock. Do you know if there is anywhere else that needs to be bled in the boiler apart from the screw cap AAV, and the Circulating pump screw cap. There is a notice on the boiler saying after refelling the hot and cold systems should be flushed through. Any idea how I do this on my type of boiler.

Tks for your time on this

Cheers
ray

 

[raycampion]

OK - have re-pressurised the expansion vessel. Still showing the same problem on start up. Is there anywhere else that needs to be bled except for the AAV?

Tks
Ray

 

[Gasguru]

Does the pump sound quiet?

Look closely at the white lever (indicated below). It should move as the pump runs and activate the red switch. If its doesn't air is still trapped in the boiler or the small control tube is perhaps blocked. I would always replace the auto air vent after de-presurising - its a standard Callefii 1/2 (just the top piece).

 

[Agile]

Its a bit of a boiler engineer's trick but if it really is only the air in the system then setting it on DHW and manually operating the flow switch heats up the system water and reduces the solubility of the air and aids expulsion of the air ( if the AAV is working! ).

Bit late now but when draining the system on a Vaillant the boiler isolating valves should be closed and then you still get DHW and the boiler is not filled with air.

Tony

 

[raycampion]

Hi Gasguru and Tony,

Tks for the replies. Ok Gasguru - i've watched the lever, and it does move clearly up and activate the red switch, but the boiler still switches off before igniting.

Tony - What is a DHW setting. Can you talk me through how to do what you've recommended.

Cheers
Ray

 

[Agile]

Tony - What is a DHW setting. Can you talk me through how to do what you've recommended.
Cheers
Ray

A DHW setting is just turning on a hot tap to create a demand for DHW !

 

[raycampion]

Hi Agile,

The boiler feeds into a megaflow water cylinder, so I'm guessing that turning on the hot tap won't have the same effect as on a combi boiler. The water temperature in the system is showing at 20 degrees now, so I guess it should already be trying to turn it's self on. Please let me know if my assumptions are incorrect here.

Tks
Ray

 

[raycampion]

Hi Guys.

Any further ideas on this one - need to get it fixed soon or wife will move out