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.
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.
I'll try switching it off as you suggest.
Check that you don't have a motorised valve that has failed, leaving a microswitch closed, faking a demand condition. Do you have a test meter and a wiring diagram, and a suitable junction box for testing power at different points of the wiring?
I replaced both the hot water and heating motorised valve motors as they were failing last year so I would hope they are OK but I'll check.
Yes I can test things with a meter and can get at the wiring box but it's awkward.
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.
You don't need to replace the water unless the pressure drops too low when cold.
Not necessarily exceptional for a "hot" system. How many rads on the system?
So you have an unvented primary (aka "sealed") system for the heating circuit, and you also have an unvented (mains fed) hot water cylinder?
(In which case there will be two separate expansion vessels - one (probably in the boiler) for the primary CH system, and another connected to the unvented cylinder.
I take it the cylinder is an "indirect" type?
Could you explain what type of control system your setup uses? i.e. Does it have a time switch or "programmer", room stat, cylinder stat, one or more two or three port valves?
If you refer to :
Once you know the layout and the control system, you now need to logically step through the controls, and work out why a call for heat is reaching the boiler when it should not be.
Its possible, however it does not explain the cycling boiler problem.
Its a fairly easy DIY job IME.
You might find this useful.
Was this ever resolved?
Replacing the Expansion vessel is actually a really easy job but you'll have to remove the flue pipe. (This is on my Turbomax Pro 828E) My Flue pipe was already falling to bits on the outside of the house so it made sense to get a new flue kit along with the expansion vessel.
Removing the vessel is simply the one wet connection at the bottom of the vessel. Take a picture of the air-pressure switch top right of boiler and remove that and poke air pipes through the back plate (making a note of which pipe goes to which connection). The expansion vessel then simply slides up and out. I say simply but it's quite a heavy lump especially if it's still got water in it (on the "dry" side of the membrane) so you have to push it up as far as possible from the bottom then grip it from the top and pull upwards.
Well I've finally got around to getting under the stairs to investigate.
One thing for certain - the motorised valve controlling the hot water was jammed half open, and the valve body has a very small leak but it seems to have destroyed the motor body, which is a shame as I only replaced both actuator heads recently (the other for the heating circuit).
So I need to replace the valve body but that's beyond me although I do have the part as I bought it with the motor actuator. But It looks like I need a new actuator...
i presume the system needs a drain down to do the valve but it's just a couple of large screw nuts.
At the same time I guess I should get the expansion vessel serviced. I think the boiler is fine - it's a bullet proof Valliant that was serviced a year ago.
I've freed the valve spindle and applied a bit of lubrication for now and will operate it manually til I find someone who can replace it and the motor head - unless anyone thinks I can do it?
serviced? It's an empty container
They can need repressurising.
Yup in principle - although it does depend where in the system the valve is, as to how much of a drain it will need (valves in a loft for example can often be change with only a partial drain down).
2 port valves are easier to swap than three port - especially if the valve is a close match and can re-use the existing back nuts and olives. In principle, undo both nuts, swap valve and re-tighten. The devil is in the detail, like how easy they are to get at, and how rigid the pipes are (i.e. will they move enough to let you get the valve out).You can check the pressure easy enough yourself. Not sure about the Turbomax, but on the Ecotecs the expansion is readily accessible and the shrader valve is right on the front right:
Its certainly DIYable... Turn boiler off, drain down, swap valve, reconnect to wiring. Refill[1], and bleed, and set system pressure, and turn boiler back on. If all looks good. The turn off again, and add some fresh corrosion inhibitor. Turn back on.
However it depends on your level of confidence and having at least some basic tools like spanners to fit the nuts etc.
[1] Vaillant boilers often have a handy test program you can get them to run at startup, that will just run the pump and show you the system pressure without trying to fire. Ideal for refilling and purging the air from the system.
Just test with a car tyre style pressure gauge... For a full test you can drain a few litres of water out of the system first to lower the system pressure. Then most[1] of what you read will be the air pressure in the vessel alone. However you can test at full system pressure - in which case, it reads about the same as the system pressure (and so long as its air that comes out of the refill valve and not water when you measure it, you are probably fine!)
[1] If the boiler is physically lower than some of the system, then you will still read some of the water pressure just from the "head" above the test point.
Thanks John. What do you think of this - it's the same Danfoss valve and as the pipework is at the back under the stairs it may be easier just to change the spindle but looks hairy without draining down. I guess easy to do if drained down and guards against disturbing pipes as the cylinder is very near.
I have never worked on a Danfoss valve, so that was an interesting vid.
It looks doable, and even if you decide to bail out and do a full drain down mid process, you should be able to plug the valve base with something to keep the water in the for duration. Easier than replacing the whole valve body anyway.
(my plumbing kit has a set of conical rubber bungs for just such eventualities. Also very useful for plugging the feed and expansion pipes on vented HW systems or vented CH header tanks to keep most of the water trapped in them)
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