Vaillant EcoTec plus 438 problem

[Coldstream]

I wonder if anyone can help - three plumbers I've had in can't!
I have an EcoTec 438 which was working perfectly. I closed off the valves on one red to remove it and redecorate a room. The heating continued to work perfectly. I replaced the rad, opened the valves and re-filled it, closing off the bleed screw when full.
From that moment, the heating is all screwed up. It may be the biggest co-incidence ever, but I cannot understand the connection.
Now, the boiler fires up, heats up very quickly to its target temp, shuts off with an S53 message for one second, then S7 - pump overrun. The rad display flashes for a couple of minutes then settles down - the burner is on, low, temp constant at 43°, then suddenly flashes another S53 and then roars on, running up to 65, then does it all over again.
Switching off the central heating (motorised valve) so that only the hot water tank is on the circuit, makes no difference - so its not a blockage in the rad pipes.
Help? I would call Vaillant, but the £220 call out charge is another thought.

 

[Mbear]

I wonder if anyone can help - three plumbers I've had in can't!
I have an EcoTec 438 which was working perfectly. I closed off the valves on one red to remove it and redecorate a room. The heating continued to work perfectly. I replaced the rad, opened the valves and re-filled it, closing off the bleed screw when full.
From that moment, the heating is all screwed up. It may be the biggest co-incidence ever, but I cannot understand the connection.
Now, the boiler fires up, heats up very quickly to its target temp, shuts off with an S53 message for one second, then S7 - pump overrun. The rad display flashes for a couple of minutes then settles down - the burner is on, low, temp constant at 43°, then suddenly flashes another S53 and then roars on, running up to 65, then does it all over again.
Switching off the central heating (motorised valve) so that only the hot water tank is on the circuit, makes no difference - so its not a blockage in the rad pipes
Help? I would call Vaillant, but the £220 call out charge is another thought.

I take it the entire system is filled & vented, ie boiler aav, all rads, pump, any extra system aav's maybe at the cylinder or near zone valves?

Shot in the dark(without seeing it in action) It may be a burnt out pump, does it make loud banging noises when the fault happens?

 

[Coldstream]

Yes, thanks for the speedy reply.
We have had the entire system drained and refilled - at one time the plumber actually connected the mains to the return and blew everything out. The system is now full and bled all over. Its a brand new pump, put in this afternoon in desperation.
With being on all the time, up and down, the hot water tank is warm, and the upstairs rads are warm, but I think this is due to convection (or whatever!) and the return is still cold.
There is an 'emergency bypass valve' (?) after the pump and straight on to the return, so if there was a blockage, it would surely come into play, but it hasn't. Besides, when the CH is off, and only the HW cylinder calling for heat, the boiler reacts in the same way.... so I cant see it being a blockage anywhere else but in the boiler itself - is this possible?
Sorry, but what's an aav?
Thanks again.

OK, so I googled aav and now I know.
No, we dont have any - the system is not pressurised, with a cold water header tank and an open vent.

 

[Mbear]

Automatic air vent mate.

I've not repaired many vailiants recently(they are usually very reliable boilers, therefore u don't see them that often), is ur boiler a combi or system version?

Ok it's open vented then.

Ok how old is system? And boiler if different age?

There's a possibilty that you've got either an airlock on the return Seeing as it's been drained or a choked cold feed. Id say guessing airlock as you've drained a rad and refilled. I'm having a nitemare with something similar myself at the min. What did the plumbers say?

If u have a look at my thread 'nitemare airlock' in this section and you can read the things I've been trying to do to clear an airlock the last 2 days. It can be horrendous and very very time consuming mate

 

[Coldstream]

The system is about 20 years old, running beautifully on a big old glow worm, then 2.5 years ago we went all PC and had installed a eco-friendly load of trouble. We had lots of problems before with the S53 problem (NTC sensors) which even the local Vaillant-appointed engineers could not fix. I read all the books, trawled through these forums and then ran the output down from 34Kw to 30 and it was fixed - perfect - for six months until now !
With only HW on, between the boiler, the pump, the HW cylinder and back to the boiler where can the blockage be? There is a vent screw just before the return enters the boiler which bleeds water under pressure. And with the HW off and the CH on its just the same, so there would need to be another, separate coincidental blockage in the pipework?
What did the plumbers say?
"Its got me beat!", "We're only paid till 2.00 o'clock on a Friday", I'll get the boss to phone you" and other such things.....
btw... I'm alone in this house with a wife and two daughters

 

[Mbear]

The cold feed is the most common place to choke. It's where the header tank fills the system. This cold feed 'T's into the system somehere probably close to the pump or boiler. If you are able to locate it, get an ordinary fridge magnet and see if it sticks to the cold feed 'T' or close to it. If it sticks then it's choked with magnatite, magnets DO NOT stick to copper pipes that aren't choked however it will stick if it's choked as I say

I still think you've got an airlock in the return bud

 

[jonboy]

Its a brand new pump, put in this afternoon in desperation.

Make sure it is set to max speed.

 

[dkleeman]

I think that I have a similar problem on this boiler. The heating cycle ends very quickly after the temperature shoots up. There is some white crud around the flow isolation valve which makes me think that this valve might be blocked.

If it is the valve, is it easy to replace?

Daniel

 

[Coldstream]

Its been a while since I was involved with this thread, and I never really closed it off. Bottom line is, I contacted British Gas, signed up to £20 a month for the rest of my life, they came along, spent about three minutes checking, and confirmed what I had said all along, and what I had told the plumbers, the blockage is in the boiler. He replaced the heat exchanger, and that was that.
I don't believe the heat exchanger would have been blocked normally after just two and a half years, so I must suspect the boiler installer failed to completely clean out the 20 year old system when he installed the new boiler.
(btw. the heat exchanger would have been £300 if I had to pay for it)

 

[washer]

The tubular heat exchangers in the vailliant are a nightmare, always blocking up if your system is sludged, which it is by the sound of it, you might want to consider a magnetic filter on the return, BG would not replace your heat exchanger a 2nd time if it is sludged.