John Smith wrote:

On 2020-04-24 11:45:27 +0000, Roger Hayter said:

John Smith wrote:

Our old Valliant Turbomax is humming away with the central heating
light on, and every 5 mins or so firing up for a few secs and then
firing down, but both heating and hot water are turned off at the
controller.

I've noticed that the boiler pressure is over 2.5 bar.

It's an unvented system with a hot water tank and (blue) expansion vessel.

Am I right to suspect the expansion vessel - it either is failing or
needs recharging. I guess not a DIY job.

You have a problem with your control system or wiring, as this should
not be happening if both hot water and central heating are off. Do you
actually get sustained hot water if you turn on the tap while the hot
water is nominally switched off.

It seems likely the expansion vessel has failed, but to confirm this it
would be useful to turn of all electrical supply to the boiler, let it
cool down, and confirm the pressure falls.

It's an unvented system with a hot water tank so of course it delivers
hot water as long as there's some in the tank.
Yes, sorry I'm confused. But the boiler still should not be cycling if
the hot water is off and the CH off. And there should also be a way of
preventing it doing so when the water thermostat is not demanding heat
in a modern compliant system.


The heating and hot water are working normally otherwise.

I've tried bleeding a rad taking out a litre or so and that drops the
pressure to about 2 bar for a bit. I presume I'll need to open the
filling loop to replace the water though and that raises the pressure.

You don't need to replace the water unless the pressure drops too low
when cold.



I'll try switching it off as you suggest.


--

Roger Hayter