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
Any recommendations for things to try?
It is possible that either the normal thermostat or the cut-out has
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.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
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
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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
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].
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.
Yes, an auto by-pass is better - because it will *only* open when the water
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!
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
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.
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.
That's ok as long as you haven't got additional heating in the lounge - such
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.
Why have central heating at all - if you only want to heat the room you are
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.
That will probably solve the immediate problem, but may not be a very
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].
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