SIME Boiler - no DHW but loadsa CH

I have a five year old Sime boiler - not sure on the model Super 4000 or something - If it is set to CH only it generally works OK but occassionally stops heating and won't come on until boiler is turned off cools and starts again. DHW works initially but flame failure occurs after first thermostatic switch off. You can reset and it will fire but same thing occurs in ever decreasing time periods. We have had a CORGI registered man looking at it and have had the gas valve replaced, burners, clocks and pumps are fine. The problem seems electrical - he suggests replacing the ignition box at £300 but cannot guarantee this will fix it. Could the thermostats be involved - how should we proceed? Any advice welcomed.

Paul

when you say reset it do you mean it locks out.
I may be on the wrong track but it sounds like its overheating. what happens when you have heating and hot water together. do you have motorised valves are they ok if yes.

I cant understand what difference it makes to the boiler whether its heating rads or cylinder apart from the fact that the cylinder heats quicker so the water returning reaches temp quicker. unless the boiler stat is faulty or has that been replaced.

Thanks for the reply - it does seem like it is overheating but the thermostat cuts in and if on water the gas valve is not opened, if on rads only then the boiler sometimes does not restart - ignition fires (you can hear the piezo clicking) but there is insufficient gas - no circuit made on the gas valve - this only occurs after thermostatic cut-out. Once the gas valve has not opened the boiler locks down and the pilot light comes on - there is a reset position on the controls - water, water+rads, reset. You must reset and then the burners fire.

If you run water and rads together, water has priority and the cut out/flame failure occurs.

Truth is I have no idea how the circuits are switched and what is thermostatically controlled or where...

All the motorised valves seem OK - flow of water seems OK although there are some small leaks and the non-return valves seem functional. The pumps seem OK but everything seems to be running extremely hot - too hot to touch.

The model is a "super four" and the ideal would be a circuit diagram to aid the diagnostics - we are getting desperate and we have been quoted £2300 for a new condenser boiler - I'd rather buy a big kettle!

I too have a SIME boiler (100E)- 4yrs old partially the same problem. Seems to overheat. Everything but the pump/fan shuts down - NO Hot Water. Switch the system off/on manually and it all starts working for a while(up to an hour depends on temperature setting). Fortunately on contract, but have had circuit boards replaced, pressure switches and new fan. But still the fault persists!! Any ideas?

pwhitfield said:

The problem seems electrical - he suggests replacing the ignition box at £300 but cannot guarantee this will fix it.

Click to expand...

if he can't find the problem i suggest you get someone who knows more about those boilers or you're gonna get parts replaced until it's fixed.......at your expense.
i would never suggest it might be something, i would take the time to test it and be sure.

My problem solved. The PCB that controls the electrics now replaced.

I have had similar problems where the boiler stops firing and the engineer has replaced the ignition board and according to his records this has been replaced approximately every two years since the boiler was installed. This doesn't say much for the quality of these boards.

I am presently having a problem with the loss of water pressure on the CH side. I have fixed a couple of leaks but still can't find where the problem is, although I am beginning to suspect the pressure safety valve is leaking.
The boiler runs ok until it switches off at night then pressure drops very quickly. Recharged the pressure stays up during the night and fires ok in the morning then the pressure drops again the next time it goes off.
Anyone else had this problem?

The problem you are having is likely to be a leaking tyre valve located on the red pressure vessel below the boiler. The tyre valves are not designed for the temp that they are subjected to and leak.

replace it and put a metal tyre valve cap on. then pump up the CH presure to 1 bar. Make sure that you get some air in since the vessel is designed for half air half water.

My problem is the boiler fan spins for a few seconds then turns off. this goe's on for say ten cycles then eventually the boiler fires. then all is ok for a few days until it repeats. I'm suspecting the presure switch but when I gentle blow down the pipe I can hear it clicking. any ideas?

Has any serviceman taken the burner out of the boiler?
I sould say that after 4 years of operation having such a serious problem would justify a complete teardown and inspection of the boiler including removal of and inspection of the burner( any holes and it MUST be replaced) and a full inspection of the heat exchanger and flue passages.
At this point you should have it done annually by somebody that specializes in hydronic heating. This annual inspection should be done for functionality AND for SAFETY reasons. Don't let a few bucks get in the way of your safety. Carbon Monoxide kills.

Hint: Don't look for the lowest hourly rate. It is meaningles if the person does not know what they are doing and will ultimately cost you more money by replacing unneccessary parts and making numerous unneccessary trips.

If your boiler has not been completely openedf up at this stage the person is not doing their job properly.

regards

I dont think that Hydronic Mike knows anything about Sime boilers or even any of the normal heating combi boilers used in England!

The burners are NOT designed for repeated removal and it would be unusal to ever need to remove the burner duringthe lifetime of a unit!

Tony

its the ignition box