worcester 280 combi h/w

Please help,having problem with intermittent h/w. Boiler comes on for 30 secs then turns off for for 30secs.Works o.k on c/h.Previous engineers have changed h/w heat exchanger,pump,p.c.b & h/w sensor .Still same problem!!!!

Previous engineers have changed h/w heat exchanger, pump, p.c.b & h/w sensor .Still same problem!!!!

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They are not engineers. Engineers will work out what is wrong and fix it. People who randomly change parts until by chance they hit upon something that works are called "parts changers". Do not pay them any money!

Having repaired loads of these, the problem sounds as though the boiler is shutting down and cycling because it's overheating in Hot water mode. Now, my guess is it's the gas valve not modulating properly. As he's changed the PCB and hot water sensor I would put a pound on it that it's the gas valve.

Regards James

yep probably agree on the gas valve....there isn't really anything else left. Did the new hot water sensor improve matters briefly?

Very much doupt its the gas valve not modulateing as the 280 is not that responsive, more chance of poor circulation .The gas wont start to ramp down untill the hot water gets to above 55 degC so if your eng tests the hot water temp comeing out of the boiler while manometer atatched he will see if its modulateing or dropping out. The primary senser is prone to failure as it gets heat damage if the iner combustion front isnot fitting fully, you can often see the scorch marks (its allso the ch sensor fitted to the gas/water heat ex) its easy to test just swap it with the new dhw sensor as they are the same spec ,if its faulty the problem will change. The 280 allso has a steel back plate with lazer welded chanels for the plug in components (pump heat ex etc ) so if this is blocked your in fo a new boiler as its to costly to replace and cleaning can often leave pin holes.

I think you have missed the point.

If the gas valve is not correctly set for max and min gas pressures then there will be little or no modulation taking place regardless of what the controller is trying to do.

Is this the one that needs a 2 mm and a 3 mm Allen key? A real pain when other valves use standard tools and you have lost the 2 mm key!

Tony Glazier

280 uses a honywell gas valve so small spanners req to adjust but as said test it before changeing ,both corgi eng jobs. min is 2.0 max 14.0 if on NG