Worcester 280rsf? Boiler, hot water, no hot water.

[jotto]

Have a problem with the combi boiler, most noticeable when having a shower or when trying to run a bowl full of hot water.

The boiler can be heard to kick in and we get hot water, then the boiler cuts out and water cools, kicks in hot...drops out, cold!

Real PITA.

Pressure in Central heating side seems constant. Doesnt seem to be boiling within the boiler, had a faulty pump before which would boil up and throw the thermal overload.

Any ideas where to look or what to check first?
Thanks in advance.

 

[jotto]

Could it be that the water is getting too hot so the boiler cuts out and then cuts back in when it senses it has cooled enough? If so, what would be the likely cause of this?

OR

Could it have anything to do with the expansion vessel? I know we had a pressure loss issue and someone said it could be the pressure vessle but this would have to be checked and recharged if necessary ONLY once the system had been completely drained. Can this only be checked with a drained system and what should the pressure be in the vessle in this model?

Thanks.

 

[fazedup71]

when you run the hot tap if you turn the temp down on the boiler does the flames go down? does the boiler work ok in central heating mode? could just be a sensor fault or scaled up of dirty heat exchanger, could just need a service, sometimes on some boilers fan blades get dirty or the venturi gets dirty and it cannot maintain air pressure switch, those are the simple things i would be checking first

 

[jotto]

when you run the hot tap if you turn the temp down on the boiler does the flames go down? does the boiler work ok in central heating mode? could just be a sensor fault or scaled up of dirty heat exchanger, could just need a service, sometimes on some boilers fan blades get dirty or the venturi gets dirty and it cannot maintain air pressure switch, those are the simple things i would be checking first

Will check the flame and temp control. Are the other items sapart from a service something a handy/competant person like myself can do, ie strip down and clean? Am a sparky by trade and am mechanically minded.

Is there anything i really shouldnt be opening up?

 

[fazedup71]

first thing i would check is thermister, the plate to plate couldneed a clean but that migth be tricky for you to take out and might need new seals so best not done today!!! same with combustion chamber front it not something you should really be touching, but certainly check sensor first, you got a variable resistor you can try instead of thermister?

 

[Agile]

It sounds to me that its more likely to be a sludged up heat exchanger.

Can you measure the flow anmd return temperature on DHW mode?

That should only be 10-20° C ! Much more indicates its probably dirty!

Tony

 

[fazedup71]

am taking it the diverter valve is working ok? no radiators getting hot when you run hot water? if yo u got good knowledge of electronics etc then test away! half the clowns that might come to look at your boiler could not even do a continuity test let alone understand ohms law! A scary world we live in!!

 

[jotto]

Diverter valve is fine and working correctly. I am pretty competent with the old Ohm meter so can check.
Have a temp sensor somewhere that plugs into the multimeter...will check temps of flow and return.

What would be the maximum allowable difference on flow and return pipes?

Will check the documentation that I have. Is there a schematic of the beast I can download from somewhere?

 

[jotto]

OK, had another look today, the difference in temp between flow and return if Im measuring right is very much, wrote it down somewhere...

After looking around a bit, I removed the cap from the pressure vessle and pressed the inner point to release a little air to make sure there was pressure there. WATER came out! I guess I need a new vessel. Could this partly be the cause of my problem?

Wife was having a shower and it semed like it was cycling on and off continuously.

When heating on, boiler stays on and remains on...

Will check heat exchanger when I replace the vessel. Pretty sure scale will not be an issue as we live in a very soft water area and Ive yet to see any build up on out kettles or washing machine elements when they have needed replacement!

Any thing else I need to look for?
Thanks.