baxi bermuda back boiler heating on full bore

15 Oct 2012
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United Kingdom

First post so sorry if I mess up.

We have recently just purchased a property built in the mid '70s that has a back boiler & I am told it is a Baxi Bermuda.

The problem is even when it is set to hot water only the central heating comes on full tilt & regardless of whether it is set to central heating or hot water only the thermostat on the wall in the dining room does not have any effect with rads being too hot to touch.

Any idea would be much appretiated
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A lot depends on how it is plumbed and wired up.

Could be the 2-way valve actuator has jammed - not responding to roomstat makes this likely.
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Thanks very much for all these speedy replies I do appreciate it...

What is a F&E tank?

How would I tell if it was full?

my baxi back boiler was plumbed up as gravity hot, pumped CH and no zone valves.

if you can't find any zone valves anywhere (which you could trace the electric flex cables as well as just the pipes, they should point to a zone valve)

then mine was setup as follows:
timer was wired up so boiler comes on with HW setting, this would heat the hot water cylinder alone.
the pump came on with the CH setting (thinking being is the pump acts a makeshift zone valve when off)

it didn't however have a room or cylinder thermostat, we just had lots of TRV's and a setting on the back boiler itself.
No sure where they go they just seem to connect to other pipes that connect with upstairs.

Does that help?

a diagram of the system or wide pictures would help immensely.
even if it's to floor level.

p.s. on the side of your timer/clock, there are two black toggle switches,
it's too blurry to tell but are they marked up HW & CH ??

if it is, have you tried with CH off?
have you got a picture of your room thermostat?

depending on the back boiler, there should be a flap under the fireplace, this has the boiler controls on, if it's on full there, try turing it down.
that's the boilers internal thermostat and stops the water getting scorching hot before it stops firing, i had mine running at 2 out of 5 most of the year and only when it was really cold did we turn this up.
Thanks again for the replies I am not in the house at present so supplementary photos are awkward but I can answer the questions.

The time clock does has CH & HW and set to HW only the central heating does still come on full bore.

The room thermostat is the same goldish brownish square affair with a circular dial in the middle that seems to be in every home I have owned.

Does this help?
can't confirm that the HW is gravity myself from the tank photo, needs to be wider angle so we can see full extent of the pipes in the bottom left.

if it is gravity, then the pump shouldn't be needed when HW is ON as thermosyphoning should take over, pipework to the HW cylinder would be an inch or more in diameter (28mm) constantly rising to the hot water cylinder with the feed and vent being smaller and leading into the ceiling.

if it's not gravity then there should definitely be one or two zone valves as pictured up above to control what gets hot water from the boiler, could be the CH one is jammed open.

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