I have a Baxi 105HE combi boiler.
When the hot water is in demand the boiler will run ok no matter how many times it is required
However when the selector is placed to the heating position, the boiler will heat up to the required temp but when it goes to re-heat it ends up locking out and the fault light on the 30degree lights. On trying the reset switch, it relights but after 2 or 3 attempts locks out and the boiler will not reset until the temp drops back to around 40 degrees. I have all ready changed the condensate drain and this drains ok. Ihave also now changed the central heating temerature sensor, the safety thermostat on the heating side and also the pcb.
None of these have solved the problem.
Any one any ideas on where to proceed from here?

paul keenan, November 2008

Just changed Diverter valve and expansion vessel... this cleared original faults but now dhw is fine but CH wont stay on... runs for approx 6secs then drops out (was a full flame) seems to repeat this after reset or mains switch off. This is first time in 6years a prob has occurred. Any ideas please

Tim coldfinger, March 2011

fantastic ! glad i could help out

matt, November 2008

Got someone to adjust the low pressure on the gas which he did and the boiler is now working properly.

Many thanks for your time and help

Paul Keenan, November 2008

to check the low setting run the heating and pull one of the black wires off of the top of the gas valve [this will drop it to low and will stay like this until it is put back on] ,it will be around 1.5-2 mb adjust it to 3mb and see how u get on

matt, November 2008

The hot water runs ok....I have a teenage daughter who should be a fish the amount of time she spends in the shower which runs off the boiler so not been any problems there!!
So I take it that may be the gas valve that needs adjusting so I'll have a word with a friend to come check the gas pressures...thats one thing I won't play with and i'll let you know how he gets on.

Many thanks for your help so far

Paul

Paul keenan, November 2008

i would get that low gas pressure checked , when the heating first comes on because its cold the flame will be on high, as the temp rises the flame modulates down to the low setting , the flame detection probe will detect the high flame because its taller but the low could poss be too low and its not being detected by the sensor , the hot water also uses the high flame , so poss explains why the hw is ok ? if the hw is run for a long time it will drop to low flame at some point tho , does it lock out after long hw use ? [1-3 mins ]

matt, November 2008

The green light above the tap does not come on when either the boiler is first turned on or reset with the taps closed.
When placing the selector switch to reset, the flashing 30 degree light goes out then they return to the temp of the water and the radiator light comes back on.

The boiler lights ok in the ch mode and remains lit untill the water temp has been reached. It is when it goes to reignite to keep the water at the desired temp that the problem occurs (this does not happen when boiler is in just the water mode...the tap can be opened and shut numerous times and the boiler lights normally on all occassions)

The boiler reignites for approx 5 secs then a click is heard and the flame in the glass panel of the chamber goes out. it does this 3 times then locks it self out.

This happens no matter what temp is selected on the ch temp control knob.

paul keenan, November 2008

when you turn it on or reset it does the green light over the tap come on with all the hot water taps closed ?

b, November 2008

the 30 degree light is flame failure .. is the boiler lighting up in ch mode or trying to light ?... it is common on these boilers that if the low gas setting is too low and will not be detected by the sensor , its ok when its on high .

matt, November 2008