baxi bahama 100

Hi, Can anyone help I have the above boiler which cuts out on over temperature, I have replaced thermistor and overtemp stat and central heating flow switch none of which have solved problem. This is a intermittent fault which makes things worse sometimes you can reset and bolier will run for three four days other times it will trip three or four times a day, I have checked the temperature control pots they are working ok. I am an electrical engineer to trade thanks for any help.

Reply to
brian
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Is it a fully pumped system, and does the boiler need to control the pump in order to provide over-run (i.e. to keep the pump running for a bit after the boiler stops firing)?

If so, is it wired up correctly for doing this? During pump over-run, is there always a path for the water to take? [There may not be if it's an S-Plan system without a by-pass circuit, or if all rads have got TRVs which are closed].

We need a bit more information about the way in which your system is plumbed and controlled in order to be able to comment further.

Reply to
Roger Mills (aka Set Square)

Hi Roger, The system is fully pumped and has been running properly for the last seven years the fault only started around Christmas.

Regards Brian

Reply to
brian

OK, so *does* the boiler control the pump? How many motorised zone valves are there, and of what type? [Likely to be one 3-port valve (Y-Plan) or two 2-port valves (S-Plan)] Are all of the radiators fitted with TRVs? Is there a by-pass circuit? If so, is it manual (adjusted by gate valve) or is there an automatic by-pass valve?

Did you make any changes to the system shortly before the problem started, such as:

  • adding TRVs
  • adjusting gate valves
  • turning up the boiler thermostat?
Reply to
Roger Mills (aka Set Square)

Hi again, The boiler does control the pump there is one motorised valve y plan all except one radiator are controled with TVR's this being the expansion for the system, and no there were no alterations or mods done to system.

Cheers Brian

Reply to
brian

[It would be useful if you were to quote at least part of the message to which you are replying - as I have done above - so everyone knows what you're replying to. *I* know - because I asked the questions which you're answering - but others may not].

If the overheat trip operates, there are only two basic causes: Either the overheat stat itself is faulty, or the boiler is *really* overheating because there's not enough flow through it to carry away the residual heat after it stops firing. If all the TRVs are closed, there not be enough flow through the remaining radiator - particularly if it's partially turned off manually - to keep the boiler happy.

Do you have any means of measuring the flow temperature when the boiler is operating normally? If the main stat is allowing this to be too high, there may not be a big enough margin between the normal and overheat temperatures. You could try turning the main boiler stat down a bit - that often helps. Even a couple of degrees from (say) 82 to 80 might be enough.

Do you have any means of checking the operation of the overheat stat? I checked mine by pulling the bulb out of its pocket and putting it in a mug of hot water. I heated the water further with a mini-immersion heater and, using a mercury in glass thermometer, noted the temperature at which it tripped. Mine tripped at 95 degC - which seemed about right.

Reply to
Roger Mills (aka Set Square)

"If the overheat trip operates, there are only two basic causes: Either the overheat stat itself is faulty, or the boiler is *really* overheating because there's not enough flow through it to carry away the residual heat after it stops firing. If all the TRVs are closed, there not be enough flow through the remaining radiator - particularly if it's partially turned off manually - to keep the boiler happy." Sorry Roger thought I was only talking to you new to this group thing.I have checked the overheat stat and the temperature control and although they were both working within Baxi's recommended resistance against temperature I replaced both. But you may have struck on something I had forgotten the flow on the central heating return there is a in line gauze filter which has blocked before not causing this problem cannot remember exactly what but it was blocked quite badly restricting flow. I will check this to-morrow and let you know how I get on. Thanks for your help Brian

Reply to
brian

Hi Roger, In reply to boiler overheat problem where you suggested there were only two basic causes, either overheat stat which I had already replaced or the flow through the boiler this I investigated to-day and found the filter in the central heating return was nearly completely blocked this I have cleaned and have had no boiler trips since . For anyone who has a Baxi Bahama 100 looking at the front of the boiler the filter can be found in the first pipe on the right handside the one which goes into the pump. To access filter first turn valve on this pipe off ( anti-clock ) then release pressure from boiler relief valve extreme left the valve with red plastic cover turn anti-clock until all pressure is released a few seconds. Now you can split coupling below pump and access filter after cleaning and replacing tighten back up coupling open the valve back up and then top up water again in expansion tank. Hope this is of some benefit.

Reply to
brian

Good - glad you've fixed it! I couldn't have diagnosed the exact problem because I'm not familiar with that boiler - but if my reference to lack of flow helped you to diagnose it, I'm glad to have assisted.

Reply to
Roger Mills (aka Set Square)

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