Vaillant ecotec plus 428 help please!

20 Jan 2016
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United Kingdom
Hi all

First post - hoping someone might be able to help..

I've just moved into a house with a Vaillant ecotec plus 428 boiler installed. Problem is the radiators are getting warm but not hot (and its freezing at the moment!). I've tried bleeding all of them but no joy.

When I reset the system is comes up fairly quickly with an S53 error and if I look in the faults log it shows F22 as the last 4 faults.

Is this something easy to resolve or do I need to sell a kidney and get Vaillant in?

thanks for any help!
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Thanks Dan - looks like thats something I can't do myself then - appreciate the quick response. Would you advise getting Vaillant or an independent (I'm near Ilford)
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Have you bought the property? Do you know anything about the history?

You could look at the d0 and d1 values when its running the CH and see what they are showing. They are the flow and return temperatures.

You could also tell us the pump model and what setting it is on.

Also describe the property so we can consider the heat loss. That size boiler is suitable for a 5-6 bedroom detached house! It may be seriously oversized.

Generally unless there is an expensive part involved we would recommend finding a good independent.

This is a 6 bed detached house (though small rooms and I've converted one bedroom into a large ensuite). About 13-14 radiators all in.

i've bought the property (and seems like every little thing we look at has issues that need sorting...)

d0 = 24
d1 = 5

There's a shower pump upstairs next to hot water cylinder (aqualisa mach 250) but no other pump. I'm also about to fit a second pump downstairs as gravity fed system means that hot water downstairs takes about 2 minutes to arrive and is a slow trickle at best.
Last edited:
Sorry, I should have asked you to look at d40 and d41. ( Was eating my breakfast! )

d0 is the power output the boiler is set at. That may be better set to about 18 kW.

Its the heating pump I am interested in.

D40 = 50
D41 = 40

don't laugh - but I can't find the heating pump.
Your pump is probably close to the cylinder. It could be a rusty red Grunfoss?

That d40 and d41 indicate there is probably an adequate flow round the system.

found it - you're right! Its a Grundfos with the following numbers on it
UPS 15-50 130
230V 50Hz 2.0 uF
P/N 96281428
PC 0721

there's a small table on it which says:

v1(A) P1W
0.16 35
0.2 45
0.23 50
Most would say that as a minimum with that boiler you need a Grunfoss 15-60.

But the small differential may indicate you have a manual bypass which is too far open. It should have an automatic bypass if you have all or mostly TRVs on your rads.

thanks Tony - you're a star.

most if not all of the radiators have thermostatic valves on them - in terms of a bypass, what should I be looking for?

also I've been advised to fit a Stuart and Turner twin impeller pump downstairs to sort out the hot water pressure downstairs which is currently nonexistent.

Would I need this AND the Grundfoss pump or just one of them (and a bigger one)

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