Worcester 240 ???????

[new-bi]

Hello,

I seem to have an problem with my Worcester 240 combi:-
When boiler is switched on it fires up for 5-10 seconds and then the red reset pops up. Both DHW and CH are cold. Ther boiler seems to make a hissing sound just before it cuts out.

Things I have checked:-

1) circulating pump gets very hot but is working.
2) pipe to expansion vessel also gets very hot and there is some pressure in the vessel. (how musch pressure i dont know??)
3) diverter valve looks like it working
4) I've changed the PRV as it was leaking (Not leaking any more).

Please someone help. I'm getting desperate for any ideas?????? May be an air lock in the system ????

 

[Slugbabydotcom]

1a. A hot pump could be a stuck pump. Take the screw off and make sure the armature is spinning.
1b. Just because an armature is spinning doesnt mean that the impeller is still attached on the other end
2. If you dont know then why dont you look on the pressure guage?
3. A DV that looks like its working may not be working. Is it blocked? Is it sticking?
Does it feel as though it is working?
4. Did you re-open the valves after changing the PRV?

May be an air lock in the system ????

Could be something to do with it. Did you open the AAV at the top of the boiler?

 

[new-bi]

1a. I have taken the screw off , the armature is spinning. For the 5-10 seconds that the boiler fires up, the CH pipes below the bolier heat up.

2. What should the pressure be in the expansion vessel??

3. The DV moves when DHW is on, and the heat exchanger inlet pipe also heats up. The DV does feel like its working.

4. Which valves do I need to re-open???? (the Bolier is situated in an upstairs room, I drained the water by opening the old PRV and then replaced it.)

5. How do I open the AAV (AAV??) at the top of the boiler??? I've opened the main chamber at the top of the boiler to check if there was any air bleeding points, There looks like one point to the left side of the chamber with a black plastic screw. Is the the AAV???, how do I open it.

 

[new-bi]

Thanks for your help so far Slugbabydotcom

 

[ChrisR]

Yes loosen the blackplastic cap/screw on the Automatic Air Vent, top left.

 

[new-bi]

Thanks Chris, I've done that... no help... any idea's.

 

[ChrisR]

It could be blocked. You could try poking in the ole with a cocktail stick or similar but it doesn't always clear them. Then you have to try unscrewing the whole AAV, if it leaks water you screw it back!

Did you turn off the boiler isolating valves - open now?

Thermostatic rad valves open?

Even a weak pump should provide enough circulation for more than a few seconds..

 

[tryitandsee]

It is probably only an air lock around the primary heat exchanger (that's why it is cutting out so quickly), try draining down again and filling more slowly making sure air is being released from the AAV.

 

[new-bi]

Thanks Chris and tryitandsee,

I'll try unblocking the AAV and draining down again, and see if that works...

(Did you turn off the boiler isolating valves???) The boiler isolating valves are open as are the Thermostatic rad valves.

One question do I re-fill the system while the boiler is switched on.....or off?

 

[tryitandsee]

With out the pump running, so off for the moment.

 

[tryitandsee]

Stating the obvious, you did refill/re-pressure the system from the filling loop after you drained down and replaced the PRV

 

[new-bi]

Is there any other way!!!!!!! LOL

Anyway last night I took the pump out to check for any blockages, I bleed the heat exchanger... No errors found. Re-filled the system (from the filling loop LOL) and then retested.

No the problems still there , boiler fires up for 5-10 seconds, you hear a hissing sound and the boiler cuts out. Red reset button pops up.

Come on guys need your help on this one.

Thanks....again

 

[tryitandsee]

You never know.

It seems to be a mechanical problem!

You must be able to tell if water is being circulated around the boiler. If it cuts out so quickly, it sounds like there is no circulation of water through heat exchangers as over heat is activated. Faulty pump, airlock or blockage.

The lighting sequence appears to be doing all it should be doing.
Turn on, pump running, fan on, spark, burner ignite, flame for 5 - 10 seconds, over heat then cut out.

Hissing sound doesn't help much.

All valves opened again since last drain down! air expansion vessel at recommended pressure?

It may be a faulty overheat thermostat kicking in prematurely. Can you by-pass/disconnect it just to see if boiler carries on without it???? Unknown territory for me I'm afraid.

Amateur suggestions I know, but may get others thinking.

 

[pannierstan]

If its a grundfos pump I bet the impellor has come off the back of the pump.
You have no circulation so if there is no blockage and you are sure there is no airlocks then it could well be that.

If you turn on the boiler but leave the gas off then remove the screw from the middle of the pump and let the system run for several minutes that should definalty remove the air if you are unsure about the auto airvent.

Stan