Vaillant combi boiler problem.. no error code on display

Hi, I got Vaillant Combi boiler, installed in 2002. It has been working perfectly fine but since last one month it stopped giving hot water at randomly. so i called gas engineer he checked sensor and cleaned flame tip. It worked fine for a day and then again no hotwater. on top of that central heating is not working. I can't see 'amber' light at all. Also there is no error code on display so don't know what exactly going on. I called couple of gas engineers from yellow pages and they said they don't repair Vaillant combi boiler because of complexity.
Is any one out there who could guide me or tell me what should i do now?
Thanks.

Its a bit strange to have no heating and no hot water with no error code and a functioning display.
When you turn on a tap does the green light flash?
if yes, then press the "i" button, turn on the tap and record all the "S" codes that are displayed as the boiler goes through its demand sequence. Then post back your results. You can do this with a heating demand aswell and post these results too. We may be able to help you more then with this info.
I'm assuming you have a turbomax due to the refference to yellow light and install date.
I am interested why you didn't call back the engineer who came before??

Think i can guess why.......

Intermittantly not firing, no fault codes and you dont have to reset it.

Id start with a sticking APS. These are, strictly speaking, a safety device so should really be replaced by an RGI.

mickyg,
Thanks Mickyg for your reply. I have switched off boiler completely for half an hour and then started back with 'central heating' ON position. this has worked couple of weeks ago but now , no 'yellow' light comes on. but due to some strange reason 'green' light keeps flashing, which mean hot water is in demand but none of the tap is open. i tried pressing 'i' but again no 'yellow' light comes on and 'green' light keeps flashing.

my boiler engineer guy has charged me £135 so far (in last couple of weeks, £45/hour) first he charged me for two hour (£90), he studied all Vaillant books (because he didin't know what was the problem) for an hour and then he opened the boiler and showed me how things works. that's all he did and charnged me. On next visit he hang around for an hour, as i said that time problem was intermittent so he didn't do anything and charged me £45. so I am bit scarred to call him again. I purchased my own property six months ago so never deat with gas engineer's bill. so trying to know more before i call anyone else.

i think you misunderstood what i said. When you press "i" you need to watch the display to see what comes up there, should be some codes, "S" something.
Start with everything off, press "i", turn on tap, write down every "S" code that appears in the display. come back with your results.

You can always call vaillant for a fixed price repair if your really stuck. around £200 i think, all labour and parts.

Why do customers pay for useless boiler monkeys???????????????

Get your money back. No point in looking at the manuals...they won't tell you how to repair the design faults.

The flashing light indicates pre-heat mode is enabled. The boiler will keeep itself warm to enable a faster hot water draw-off. Read the manual for details.

Most common problem on a Turbomax Plus/Pro is the diverter valve sticking..takes all of 1 minute to check...unscrew motor head and check pin free to move in valve body.

Second most common problem is a dodgy APS as previously mentioned...takes and engineer 2 minutes to test.

Get a boiler engineer...these are about the simplest boilers to work on.

Gasguru,

Your solution makes some sense to me because 'Green' light keeps flashing though there is no hot water demand. Is it difficult to replace by myself? Because even if it is 1 minute work, Gas engineer is going to charge me atleast £45 plus parts. I know APS is difficult to replace so I would try divertor first to see if that helps, if it doesn't then I will call out boiler engineer to replace it. Cheers.

Mickyg,
Sorry, I misunderstood you. But I will try your solution to find out 'S' code. I know Vailland quote me £225 + VAT for engineer's visit. But before I call them out I just want to make sure that Is it worth to call them? thanks for your reply buddy.

The green light will only flash whilst the boiler gets up to temperature. It will then stop untill required again. This is the Warmstart feature and can be disabled by turning the hot water temperature control down to minimum for several seconds and then back up. Should save a little on the gas bill. If the diverter valve is sticking you can find the radiators warming up and the boiler firing more than it should do.

The APS is simple to test if you know how and is a common item to cause poor hot water performance (boiler won't fire up properly). Unless you know its been replaced before you could just change it. Although its a safety device its straighforward to swap (behind boiler on the right at the top).

The diverter is simple to test. Power off the boiler and drop down the lower front controls panel. Unscrew the large knurled collar securing the black motor head to the brass diverter valve (located on the left). The motor head will "unclip" with a little wiggling. Note how the actuator pin locks into the corresponding pin inside the diverter body. Now use long nose pliers and operate the pin inside the diverter...it should move very easily. If it's stuck/partially siezed or tight to move then change the whole valve.

Mickyg,

I tried to get 'S' code, but it doesn't come up when i pressed 'i' while tap was on. green light keeps flashing eventhough no hotwater is in demand. central heating doesn't warm up. any other solution you could suggest. thanks.

GasGuru,

Thanks for your reply. I could try APS test and diverter change. APS never been changed as far as I am aware of. radiators don't warm up at all. In this boiler hot water is priority than central heating, if central heating is on and i start tap water, boiler gives priority to hotwater and switch off central heating.
Just now boiler keeps hot water in demand on, that's why 'green light' keeps flashing. I could see temperature on LCD which stays on 19C. In working condition if i start up tap water, green light starts flashing-yellow light comes on(ignition is on) and temp start rising.

What I did last night-> I take boiler cover out and turn on boiler, i could see boiler ignited but spark plugs keep sparking so ignition went off. I don't know why.

Thanks for looking at my post from your busy schedual. Genius like you must be a busy man.