vailant 637 ecotec system boiler

hello
i just had this boiler installed in april 08 in a large house with ten seperate ensuite rooms and about 20 rads in total. i was told this was the best one to go for to replace a very old rickety type thing. i can see that it looks very hi tec and great but the damn thing just doesnt work properly.

i know its not the boilers fault just yet as its too soon to say but there is constantly the f75 fault and the water leaking out and pressure dropping but no leaks, which i will come back to later. suffice to say i have flushed it out and jet washed each individual radiator, occasionally i drain a bit of water and then refill and it works for a few hours enough that we can have a hot shower. but i just can't leave it without having to reset/top up water from filling loop

My immediate concern is that the external timer seems to have been wired in incorrectly. Although the installer was a family friend for many years Nic and corgi registered at the moment coz he is so busy on other jobs i am having difficulty getting him to come back as its too much travelling time and i needed to sort it asap so just thinking about paying somebody else competent and getting it sorted.

For a bit of back ground info there is a new honey well 3 way valve, the external timer and the storage tank. the installer followed the diagram in the instruction manual but when the central heating knob on boiler is turned down it all goes off (no hot water or anything) sometimes showing a f75 fault. i have read the previous logs by simon and dave in particular and both have merit as they seem to echo what the vailant engineer said that the pin 3 and 4 need to have constant live coming out and then going to the external timer. but i called many electricians and one was kind enough to spend 3 hours on the job and studied the diagram on page 23 of the installation guide and despite attempting for no charge still couldnt sort it.

Could any of you please advise how i can explain to a regular qualified electrician how these things should be wired. at the moment i have looped/bridged the 3 and 4 pins just to bypass the external timer. do i basically need two cables emanating from the boiler, 1) the twin and earth supplying the permanant live and 2) the five core/3 core cable (at the moment i have the 5 core) that goes into both the pins 3 and 4 and then feeds the external timer, three way valve and hot water tank thermostat.

Many thanks

You have a number of problems with this system.

Firstly, a 37Kw boiler should not be routed through a three port valve (assuming it is a domestic sized one) because it will act as a flow restriction on the central heating.

Secondly, if you have to constantly refill you either have a leak from the pipe network or (and more likely) there is insufficient expansion in the system. If you have a lot of rads and no secondary expansion vessel outside the boiler then you will expect to see a discharge from the emergency pressure release pipe outside.

Finally, on ecoTEC637 the lower temperature knob (with a radiator symbol) controls the outward temperature of the boiler for everything - HW & CH. So if you turn it right down, it will turn off.

I think you need to get a Vaillant approved installer round and put your hand in your pocket. This sounds like a lash up. If you keep refilling you will rust your rads to pieces and fill the boiler full of the resultant corrosion, so this isn't something you should leave.

Expect him to have to fit new motorised valves, an expansion vessel and recommission the boiler. And check the wiring. Incidentally, a qualified electrician with an significant experience should not find the wiring onerous.

I agree with all of above.

Sorry for the hijack, but I've got a Vaillant 630 boiler with problems (detailed in aother thread). Would either of dangermouse46 or simond suggest that a Honeywell 3-port valve (V4073A) wasn't suitable for a 630?


TIA,
PacketVoodoo

I don't usually fit a 22mm 3 port valve on anything larger than an 18Kw boiler. Up to 30Kw I have in the past fitted a couple of 28mm 3 port valves, but usually it is best to fit 2 port valves, especially as when you are getting to this heat output it is quite common to have several zones.

hi simon thanks for your comments. i didnt want to go into too much detail re the secondary stuff. suffice to say the leaks that drain out the system just occurred last week when we flushed out the system. a couple of radiators need changing thats all.

The installer is here now and we are looking at system. the honeywell 3 way valve has been in the central heating system/house for years and vailant engineer told me to go out and replace and i did so if i bypass the timer it all works fine. however my installer doesnt know how to wire in this particular vailant boiler so i need help as the diagram is just not right and contrary to what the vailant engineer said. could anybody advice in how to wire in the electrics to the pcb given the appliances i have (3 way valve on 28 mm pipes, tank and timer. thanks

Things just don't sound right with the installation, you can eaily bridge out the external controls as you have said you did previously, if you still have a prob I would be looking at the system setup. A system that size can be difficult to set up correctly. I would consider the previous advice of a seconadry exp vessel.

I am going to have to disagree with you, Abza, the wiring diagrams for the 637 describe precisely how it should be wired up.

Since you are in possession of these, apparently have had a NICEIC qualified person looking at it, and have also availed yourself of the Vaillant tech helpline, I cannot see what extra information you expect to find here.

My company, along with many other good tradesmen up and down the UK, are wiring this stuff up on a daily basis using the same information you have.

By the sound of of it, you have cut all manner of corners getting this boiler installed, from system preparation to the selection of the type of valves used, all contrary to good industry standards.

To install this boiler properly the system should have been cleansed ideally by powerflushing, all the radiators should be in position and leakfree, the wiring should have been tested, the motorised valves should allow a viable flow rate for the Kw output of the boiler, the system should be properly commissioned and benchmarked and gas work notified. Since it isn't working this can't have been done.

thanks for reply simon. i appreciate you being upfront but no corners are being cut. The installer who is corgi and nic registered is not cheap and has been back and we have been on to Vaillant tech support for 45 min and unable to connect rang the vailant engineer who has been out twice and he talked through the diagram and the wiring and is satisfied (over the phone that the wiring is fine). now he is that is!

Owing to lack of space here i didnt want to get into too much detail but suffice to say that the whole system was powerflushed in april 08 when the boiler was installed and then each individual radiator was removed and cleaned with hose after running x300 for a week. That was two weeks ago in an effort to rectify. as the problems have persisted i have gone through the whole system and tried to find the minutest of leaks and am replacing a few of the older rads and also the honeywell 3 way valve. The vailant engineer who came out suggested that and will come next week to double check the whole system to understand why the f75 keeps coming and i am hoping that by then it will be sorted. i have reduced the rads down to 16 now so the engineer so far has advised against expansion valve but perhaps if it continues to have an f75 it could only mean that ..couldnt it???

By the way there is no sign of leaks emanting from pipes or the over flow (or whatever you call it) that runs out into the gutter. (i dont mean white plastic condenser) so i know that the boiler is not dumping/over fill. thanks for your comments

I have to agree with Simon. Wiring a system with an Ecotec plus should be a piece of pee.

F75 is a known problem with these, but could be the result of dirty system water.

There has been a software update to try to eliminate this error code, but then your installer should know all about these known problems