Eurocombi SX20 MFFICE Overheat thermostat trips

[coolcresta]

Hi, I am a newbie here, I have signed up in the hope someone can solve my problem. This boiler has always been erratic for hot water (c/heating fine) usually down to lower pump flow on hot water, if c/heating is on the flow switch just drops enough to to cut the burner, if the c/heat is off the pin dosent rise enough to operate the microswitch, so no burner.
Now after having appeared to cure this by replacing the diverter valve (sticking?) and removing and flushing the hot water heat exchanger and cleaning gunge from boiler pipework, I now have a different problem.
With c/heat off, if a bath is run, when the hot tap is turned off the boiler shuts down normally but then the temp rises off the scale and the overheat trips, this dosent seem to happen when c/heating is on, temp just drops to 70c . This is driving me mad, I feel a new boiler coming on, sorry for the length of this post but wanted to get all the facts in.
PS I put some sludge buster stuff in the circuit as well and the boiler seems noisier now.

 

[Rob]

Guage should read about 75 degrees when in hot water.

Cant see it getting to much more unless the burner is staying alight? It certainly wouldn't shoot off the scale with just residual heat.

 

[coolcresta]

Hi, thanks for your thoughts on this, we have run some baths since I first posted but the heating has been on as well and I have had no problem.
I am pretty sure the burner had shut off when this happens but will double check, as to the temp it runs at 80-85c for hot water and 70c ish, for heating, but isn`t this dependent on the manual stats for heat and water.

 

[coolcresta]

Just to let you know I have solved the problem, I have had a Worcester greenstar junior 24i fitted!!! I would recommend this course of action to anyone with one of these boilers. After my first post it continued with the stat tripping intermittently then developed a noise like a lancaster bomber coming in to land, finally the on/off switch refused to latch, I decided to give in and get rid of it.

 

[Agile]

Just to let you know I have solved the problem, I have had a Worcester greenstar junior 24i fitted!!! I would recommend this course of action to anyone with one of these boilers. After my first post it continued with the stat tripping intermittently then developed a noise like a lancaster bomber coming in to land, finally the on/off switch refused to latch, I decided to give in and get rid of it.

Thats a pity!

All your old boiler needed was descaling! The primary heat exchanger was scaled and the heat exchange fins were overheating due to the poor heat transfer and all that excess latent heat caused the o/h stat to trip after a demand for DHW.

The noise was nothing like a Lancaster bomber coming in to land! They had four RR Merlin 27 litre V12 engines which were throttled back to almost minimum revs on landing so were very quiet. Only two left flying now unfortunately. My friends father flew 83 sorties during the war which was very unusual as most were shot down after about 20 or less. He went on to fly for BOAC/BA and retired from 747s.

The boiler noise is actually like a spitfire fighter in a full powered dive.

Its usually wrongly described by people as sounding like a jumbo jet when they describe the noise their boilers make.

Tony

 

[coolcresta]

Hi
Thanks for your very informative post, you may be right about the noise, I am of course much to young to remember lancaster bombers,my Dad told me about them!
As for the boiler I have to say I never considered a problem with the primary exchanger, but I am not a heating engineer, I am a commercial vehicle engineer, I only took the boiler on after it took 5 expensive visits from a local company to fix a hot water problem several years ago ( it was the flow switch actuator, I kept telling them!)
I think I made the right decision it really was clapped out and the family were getting pretty fed up with it.

 

[Agile]

One of the two still flying Lancasters is flown past my house on a Saturday during June every year!

Keep your eyes open for it escorted by a few spitfires!

Tony