No hot water/heating plus leak on Myson MPE222 two port valve

I hope someone can help please.

We have a Viessman Vitodens 100W conventional boiler, 5 and a half years old.

We have no hot water and the boiler is not firing up. There are no warning messages on the boiler (and it fires up and runs through the tests when power is switched on to it).

I understand from issues previously (with the radiators not heating) that a cause could be one of the two port valves or the actuators.

It has two x two port valves on the system including the following actuators:

Danfoss HPA2

Myson ACT222 (MPE222)

Upon investigating this morning, there is a slight leak on the Myson two port valve (it doesn't seem to be constant - it drips more if the hot water/heating is switched on). The dripping water is dirty (we have not drained/cleaned the system since it was fitted).

Removing the Myson actuator, it is wet around the spindle/in the unit. Is there a way to fix this leak without removing and replacing the valve please?

On the Myson, the Operating light comes on when hot water is switched on, as does the pump. When the thermostat is turned up for the central heating radiators, the boiler still does not kick in, but the Myson Operating light is on, as is the pump.

After removing the Myson (with all the power off) to check the leak there is some discolouration (and it had moisture in it) due to the water leak. Is it possible that as well as the leak, the Myson MPE/ACT222 has failed and needs replacing (ossibly an issue caused by the water leak?).

If I need to replace the Myson ACT222 and the valve, is there a way to get the boiler to heat water (as the immersion heater seems to take forever to heat up!), while waiting for the part to be delivered? Hopefully, it will stay warmer so we don't need the central heating until this is resolved.

Thank you

The valve needs to be replaced, you can’t fix the leaking spindle. As for not firing up, it might not be making the switch live. Are you able to test for voltages?

Thank you. Would it be easy for a novice to change the two port valve or by the fact I am asking does it suggest I need a plumber/heating engineer?

Unfortunately, I don't have a meter to test it, but if the Operating light is on but the boiler isn't firing up does that suggest this needs replacing too? Or is it fixable? If it needs replacing, I assume it may significantly bring the cost down if I then need a plumber/engineer to replace the valve?

Thank you

A novice could do it, but if you’re not able to confirm voltages, you could be doing half a job. Something isn’t making the switch live back to the boiler, so might just need someone in to fault find.

Thank you. I only installed the MPE222 16 months ago and it has been working fine since, so suggests it may be that. That is easy enough to change as I didn't mess it up last time .

The two port valve may be beyond my skills.

Is there anyway to get the boiler on to heat the water while waiting for a new MPE222?

Thank you

If you are saying that the boiler doesn't fire up either when the roomstat is turned up then looks like a boiler fault, is the circ pump starting as well if you request CH only??

Anon said:

Thank you. I only installed the MPE222 16 months ago and it has been working fine since, so suggests it may be that. That is easy enough to change as I didn't mess it up last time .

The two port valve may be beyond my skills.

Is there anyway to get the boiler on to heat the water while waiting for a new MPE222?

Thank you

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I be just had a thought, open up the wiring center - might be a loose (orange wire) connection. Failing that, you could put a link between the live and switched live, but might prove difficult to control.

The circ pump apparently is starting, I thought the Viessman Vitodens 100W would be a system boiler and not a heat only?

I understand they have this model that can be used as a system boiler or conventional, but ours is conventional.

CBW said:

I be just had a thought, open up the wiring center - might be a loose (orange wire) connection. Failing that, you could put a link between the live and switched live, but might prove difficult to control.

Click to expand...

Thank you for all your help. I checked the wires and all were still connected. There was water in the head, so it may have caused an issue? I have ordered a replacement as I need to replace the leaking valve before I can do anything else, as even I know water and electricity are not a good combination .

I noticed while looking for solutions (apart from the obvious - call a plumber!), that one video on YouTube for Danfoss () suggested it may be possible to remove and swap over the core from a new valve to the leaking one. Is the Myson the same steps please? It looks like it may be more straightforward than replacing the full valve, as it is fitted in an awkward position.

Thank you

Johntheo5 said:

The circ pump apparently is starting, I thought the Viessman Vitodens 100W would be a system boiler and not a heat only?

Click to expand...

Is a system boiler not a heat only boiler?
Danfoss and myson parts may not be the same
It is possible to repair the leaking spindle- have done this before

Anon said:

Thank you for all your help. I checked the wires and all were still connected. There was water in the head, so it may have caused an issue? I have ordered a replacement as I need to replace the leaking valve before I can do anything else, as even I know water and electricity are not a good combination .

I noticed while looking for solutions (apart from the obvious - call a plumber!), that one video on YouTube for Danfoss (

) suggested it may be possible to remove and swap over the core from a new valve to the leaking one. Is the Myson the same steps please? It looks like it may be more straightforward than replacing the full valve, as it is fitted in an awkward position.

Thank you

Click to expand...

Change the leaking valve is the best course of action for you

DP said:

Is a system boiler not a heat only boiler?
Danfoss and myson parts may not be the same
It is possible to repair the leaking spindle- have done this before

Click to expand...

They both provide CH only but a system boiler has a internal circulation pump and a heat only boiler has a external pump. Some manufacturers like Vaillant label heat only pumps starting with a 4, a system boiler with a 6 and a combi boiler with a 8, a 30kw heat only boiler will be a "430", a 30kw system boiler will be a "630" and a 32kw combi boiler will be a "832", the also offer a 37kw combi boiler with stored DHW known as a "937".

John the hair splitting is a system boiler is still a heat only boiler be it it has a pump and EV fitted within