Baxi boiler overheat

I've just moved into a 2 year old house and have discovered that the boiler seems to be playing up. It's a Baxi Solo 3 40 PF.
The problem is that the overheat light keeps coming on. The boiler thermostat is set to maximum but I'm sure I read that this is the recommended setting.
Any recommendations for things to try?
Thanks.....
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On Thu, 06 Nov 2003 20:26:32 +0000, Antony wrote:

drifted out of calibration. Try a lower heat setting as a temporary fix and see if this improves matters.
You should run the boiler at the lowest setting that heats the house and water typically this is a middling setting most of the time. A low setting can cause the HW to not be hot enough.
HTH
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It should be run as hot as possible to prevent condensation occurring in the burner box. I don't know why non-condensing boilers have variable setting boiler stats. Some users have them on far too low and rot their boilers away.
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Is it actually tripping, such that you have to press the manual reset button to get it going again?
If so, it is overheating because the residual heat is not being carried away fast enough after the main stat has cut the flame.
The first thing to do is to turn the main stat DOWN - it should not be on max. This then means that when it goes off on the main stat, it can afford to get a bit hotter without tripping the over-heat device.
Then check that the pump is wired correctly. This should be connected to the boiler in such a way that the boiler keeps the pump running for a bit after the boiler has stopped firing, in order to carry the residual heat away - i.e. the boiler has terminals for pump connection, driven by its pump over-run stat.
Then check that with all hot water and heating demands satisfied - but with the pump still operating to cool the boiler (as above), the water actually has somewhere to go. If the hot water and heating are each controlled by separate 2-port zone valves, there MUST be a by-pass circuit to permit circulation under pump over-run conditions. [If you have a mid-position 3-port valve, you probably don't need a by-pass UNLESS all your rads are fitted with TRVs].
HTH, Roger
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this makes sence. my baxi solo mk1 used to have to be reset regularly until i turned the stat on the boiler down to about halfway...not had a problem since. aamoi, my system has a 'short circut' between flow and return with a tap controling the flow....all rads have trv's....would it be of use to fit a auto bypass valve like what screwfix sell it the taps place? the tap system seems a crude way of donig its job.
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has nowhere else to go.
As others have suggested elsewhere, you *can* get auto by-pass valves with a pressure switch - which can be used to turn the boiler off when all the TRVs are closed. The wiring can a bit complex though!
Roger
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I think you may have a possible solution. All the rads (except one) have TRVs on them although I suspect this was something the previous owner added and not a Redrow standard fitment. This probably means that there isn't any special plumbing to handle such a situation. The only radiator not to have a TRV is the small one in the hallway where the thermostat is. Since I keep the lounge door closed, the thermostat is actually in the coldest part of the house.
Is the following a realistic scenario ?
Themostat in hallway demands heat. TRVs say it's too hot and close down although the hallway is still cooler so the boiler stays on. Since there is now only one small radiator to take the heat away, the boiler overheats because the heat cannot be taken away fast enough. When this happens, the pump keeps running even though the boiler is not lit.
Is the solution therefore to set the TRVs to maximum and turn the hallway thermostat down a touch to prevent the rooms getting too warm.
Thanks
Antony

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Antony wrote:

Wouldn't it make more sense to have the thermostat in the lounge where it can regulate the temp where someone cares what it is? Many years ago I had a house where thermostat was in the hall but I couldn't see the logic in that. In all my houses subsequently its been in the lounge.
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as a solid fuel or gas fire. If you have, that could warm the lounge and cause the stat to switch off - with the result that the rest of the house would be cold.
Roger
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Roger Mills wrote:

Ok then, put the thermostat in another room without additional heating e.g. dining room. But not hallway ... where's the logic in that?
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On Fri, 07 Nov 2003 21:33:00 +0000, BillR wrote:

Quite a bit really. The wall thermostat acts an indicator of overall house temperature this is the main control and the TRVs serve to control individual room tempertures.
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The hall is supposed have a rad sized and balanced to make it the coolest room in the house.
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currently occupying?!
Assuming that you *are* going to heat the whole house, and are using a room stat, there is no ideal position for it - and the whole thing is a compromise. You have to make the basic assumption that the system is correctly balanced and that the temperature in all rooms goes up and down more or less in unison. Thus, if you switch off the heating when one room gets up to temperature, the other rooms should have got up to temperature at the same time. It's moot as to where you put the stat. It certainly shouldn't be in a room with additional heating which is not controlled by the stat. It probably shouldn't be anywhere which is subject to large fluctations in temperature when doors are opened as people go in and out of the house. If the front door opens to the outside (without an intermediate porch) it probably shouldn't be in the hall. If there's a separate dining room, this might be a good choice.
Incidentally, I do have a porch ouside the front door, and my stat is in the hall - and it works reasonably satisfactorily.
Roger
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efficient solution. If the flow through the hall radiator is unsufficient to stop the boiler tripping, you need to increase the flow - perhaps by installing a (preferably automatic) by-pass circuit. First though, check the lock-shield valve on the hall radiator to make sure it isn't closed too much. If it is, opening it may solve the problem - and still leave the TRVs operational in the other rooms - albeit at the expense of a slightly warmer hall. [You may have to turn the stat up a bit to stop the boiler going off before the other rooms are warm].
Roger
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