I have a Vaillant TurboMAX plus 837 combi boiler which is mis-behaving.
The heating seems fine (although I may not have noticed any problems
with it I guess) but the hot water is mostly distinctly coolish
(although not actually cold). The actual temperature seems to vary
every time I switch it on - sometimes it seems completely fine but this
is getting much rarer. One confusing thing is that the temperature
display on the boiler panel claims that the temp is getting up to
around 55C as it should be.
Any ideas? Looking at the schematic on the Vaillant site, it looks
like a sticking divertor valve could be the problem though I don't
really understand the termperature display bit. Is this likely on this
boiler? If so, is it any easy part to replace?
It could be the diverter valve. The rubber ball tends to swell and get stuck
inside the valve on a Turbomax Plus due to an adverse reaction with water
additives (inhibitor etc). The new valves do not do this.
Dead easy to change.
Isolate the water to the boiler using the valves at the back of the boiler
(make sure mains water into the boiler is off - check by turning a hot tap
on, you should get nothing out).
Turn off power.
Drain down the boiler using the drain-off cock under the boiler.
Remove the diverter valve by pulling out the retaining clip, undoing the nut
and removing the plug.
Replace with new valve remembering to put new fibre washer and o'ring in.
Turn water and power back on & recharge pressure to around 1.2 bar.
NB: when removing the valve, put a cloth under it to protect the PCB
On Tue, 17 Jan 2006 06:40:14 -0800, fearonm wrote:
Temperature display is the not helpful in DHW mode, no doubt it relates to
The most probably causes are:
1) diverter valve is not going to DHW mode fully.
so with the flow pipe coolish, run a hot tap and see if the flow pipe
heats up , if it does then that's a problem. (after running the tap it may
well get hot).
2) The modulator has gone belly up. (PCB, gas valve or wiring) this moves
the rate from ignition setting say 15kW to 37kW DHW mode.
3) DHW mode temperature sensors (an NTC thermistor) which say that the DHW
is hot enough and so cuts (or cuts-back) the gas.
Ed Sirett - Property maintainer and registered gas fitter.
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