Vaillant ecotec plus 418 issue

Hi guys,

my mum lives in a council house and has had 3 different plumbers out all coming out with different faults but as it stands not one has been sorted.

hw seems fine but ch is giving all sorts of trouble she has a pumped system with the f&e tank and a hot water cylinder.

so recently the rads started to not feel as hot and has got worse, when ch is called for the boiler seems to fire up for around 30secs until it reaches 74 then stops the temp goes down to about 40-50 for around 5mins then fires up again for another 30secs and stops and just keeps on doing this, now the ch pump seems to be running while the boiler is not suggestion the water should be hot enough but the rads are only lukewarm and some colder then others.

just cannot put my finger on the issue pump seems fine, 3 port valve seems to be working it’s just the boiler but no error codes flashing up??

any ideas? Plumbers that have come 1st one just said boiler was insufficient but working as soon as he left it stoped, the 2nd said possibly pump but he will have to request a new one but said all was working so left and again stoped and the 3rd said it possibly has low water pressure so also recommended new pump but no action has been taken.

as it’s getting very cold now my mum is of age and it’s affecting her quite a lot.

would appreciate any help and advice.

Sounds like a circulation issue so pump , 3 way valve or gate valve not fully open after that restriction o heating circuit, just need to be more forceful and get them to sort it

3 port seems to be working? Feel the pipes on the A port side, find out if it’s hot or not.

Feel the pipes on the return and flow at the boiler, if there's a large differential temperature (>20C) then it's likely (not certain) that the main heat exchanger is the main restriction to flow. I have had several Vaillants (and Glowworms) develop similar symptoms. A standard powerflush won't clear whatever it is that's blocking the heat exchanger, so in your case I'd ask them to check this, and propose an exchange/new unit once they agree.

Under normal operation and loads the burner should modulate low enough that it doesn't extinguish until the timer or stat is satisfied.

Hi guys thank you so much for the reply’s, all the pipes around the pump and 3 port valve are very hot, I will check the pipes under the boiler today.

I've got a 418, it overheating too quick after firing up will be related to flow.
1. Does the boiler kettle?
2. Isolate the pump and remove the head check that impeller is all clear, I've had magniite flakes get stuck in mine and eventually killed it as started to have no torque to move water around.
3. What pump is it, does it have air vent on the front, if so take if off see if pump is spinning properly when it starts, also put screwdriver on it and check it has good torque, should not be able to stop it easy


If the above does not flag anything then ide say HE is blocked, mine did same as no magnaclean was fitted when first installed on a dirty system and also service failed to put inhibitor in the system.

I litrally just changed my 12yo pump for new one last weekend due to symptoms you mention and pretty much resolved anything.

Temp fix is to lower d00 setting to prevent it getting too hot, many 418 are not setup correctly for house size and easy to overheat.

Note the 418 has pump overrun, it will continue the pump for x mins after boiler turns off.
What you are seeing is anti cycling mode and probably flow return temp imbalance. The display code will tell you what state its in S7/S98