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Vaillant combi boiler thermostat is in red how do i fix it

F23 and water heat up for a couple of min's and go cold again

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  • Anonymous Dec 19, 2008

    Fault code f23 on vaillant combi boiler. boiler then switches its self off, requires re setting. Water has now started to run cold very quickly when system is functioning, and radiators not very hot.

    No one can seem to find a problem

  • Anonymous Mar 14, 2014

    vaillant combi no heat or hotwater

  • Anonymous Mar 14, 2014

    vaillant combi no heat or hotwater

  • Anonymous Mar 14, 2014

    vaillant combi no heat or hotwater

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  • 17 Answers

Sounds like the small heat exchanger that heats water is blocked would advise removeal and cleaning with mild acid mixture taking all the necesssary precautions of course

Posted on Nov 27, 2008

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I have a Vaillant Combi boiler, recently serviced by British Gas, given all clear. Problem we are having is the downstairs hot water tap it is a mixer tap, the cold water is fine but the hot water is


Boilers are inherently dangerous for the average DIY for so many reasons, contact British Gas and have them come back and fix it, tell them it was fine before the "service". They may simply have a control valve shut off.

Sep 23, 2014 | Water Heaters

1 Answer

Vaillant combi boiler no hot water


Is it electric? Do You have power? Is the temperature setting on high setting?

Sep 20, 2014 | Water Heaters

1 Answer

Hot water is flowing from the water heater into


boiler type? Combi,standard,if your boiler is a combi the non return valve onto your heating line may be defective thus hot water slippng back through cold line best of luck

Oct 27, 2009 | Water Heaters

1 Answer

Combi Boiler gives CH but not HW


Combi boilers have many moving parts compared to conventional models so must be serviced annually to prevent breakdowns.

Your boiler most likely has one of four problems:-

1. When the receiver for the wireless thermostat was fitted, other wiring was loosened and has come adrift. It's a possibility, but in my experience unlikely as the wiring involved isn't anything to do with HW supply..

2. During receiver fitting the pcb suffered a static electricity surge. Possible, but unlikely as this sort of damage is usually immediately evident. However, boiler pcb's are notorious for sudden failures anyway and can happen anytime. Combi pcb's are more prone to fail as they usually have up to four solenoids fitted and these do eventually fail due to mechanical wear.

3. When you your combi is in CH mode it heats the primary water circuit and directs the flow through the CH heat exchanger. When you open a hot tap (US=faucet) you're opening a supply of cold water initially as there is no stored hot water like in a conventional system. As the water starts to flow through the combi's diverter valve there's a pressure drop which activates a rubber diaphragm with mechanical connections to other parts. The diaphragm is one part which is routinely replaced annually as it will eventually fatigue and fail with the symptoms which you describe. In addition, the mechanical parts connected to the diaphragm pass through various seals in order to activate at least one micro switch. If the seals fail then the moving parts eventually corrode and seize up. Regular servicing prevents this. Combi seizures are a very common complaint in hard water areas.

4. One of the micro switches activated by the diverter valve has failed. Possible, but not likely. The purpose of the switches is usually to fire up the boiler to provide HW when the CH is not currently running, but as you haven't said which Vaillant you have I can't be definitive on this.

One major problem with combi boilers is that multiple failures can and certainly do occur almost at once. Unmaintained units may appear to be correctly functioning but in reality a number of worn parts can be close to failing. When one part fails, the others can't cope with the stress and fail as well.

In most civilised countries including the UK it's a criminal offence to attempt most repairs yourself unless you're qualified to work on gas appliances, so you need to find a decent heating engineer to service your boiler (ask your new neighbours). In the UK you can expect to pay around £120-£150 annually for a routine boiler service. If the circuit board has failed then it can easily add over £100. If parts inside the diverter valve/manifold have seized then you can be looking at an additional £80-£150. Note that diaphragm failures on their own do not merit diverter/manifold replacement and that if you have a new diverter fitted then a new diaphragm will already be present inside.

Dishonest heating engineers always diagnose a failed pcb as they know that you have no way of knowing whether it's true. If you can live with the problem for a few days then failed pcb's are usually a straightforward repair and there are plenty of companies who will send you a guaranteed exchange unit for much less than the cost of a new one. As long as you are not opening the main boiler casing which houses the combustion chamber and gas valve assemblies then some territories allow non gas qualified replacement, but others insist that the work is done by a qualified electrician: this is not the case in the UK as long as the pcb is not connected directly to mains electricity (no modern domestic ones are).

Oct 13, 2009 | Water Heaters

1 Answer

Vaillant ecoMAX 828/2boiler goes on & off when running hot water!


water must be set at 3lts a min ,check diaphragm valve move when hot tap is on, check microswitch ,best of luck

Aug 09, 2009 | Water Heaters

1 Answer

Vaillant combi boiler,dirty water comes out of hot and cold taps ,just been serviced by british gas,could you tell me the problem


Hi ,

Can you please tell me the model of the vaillant, and the approx age?

I can solve this problem

I await your reply

Thanks

Steve :)

Jul 16, 2009 | Water Heaters

1 Answer

I can't turn the bar pressure up on my Vaillant VCW 221 Boiler


on the pipework below there may be a silver braided hose with one or two valves on the end. turn the valve(s) so the handle is inline with the pipe this will allow water from the mains supply into the heating circuit , remember to keep an eye on the pressure gauge. fill the system to 1bar cold then shut down the valve(s). turn on the boiler and it should be ok, if you lose pressure again then you may have a leak somewhere which needs to be found.

Mar 25, 2009 | Water Heaters

1 Answer

Vaillant 831 combi boiler timer help


check to see the time clock is set with the clock symbol. there are three settings on analog clocks I , O and clock the I setting is constant running, the O setting is off and the clock setting is timer.
also try setting the thermostat up higher to see if the boiler fires.

Mar 25, 2009 | Water Heaters

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