Vaillant VCW-sine18 T3W burner on all day

[Kevlar13]

Had some problems recently, not firing up first time, had to turn off and on 4 or 5 times over couple of hours to get started and it ran with low burner flames all day. Incidentally use TRvs and a timer.
Had recommended engineer who checked it out then renewed flow switch and differential diaphragm. Now it starts every morning and burner fires fine, but then settles down to low flames and runs like that all day, radiators are hot enough. It used to fire on and off regularly throughoout the day
He said I will probably need a new boiler soon.
Question 1 is this going to send my gas bill sky high or will it not make too much difference as it is on low.
2. I am thinking of calling him back to try to sort this further but is it worth it
3. Should I use till summer then get a new boiler
Thanks for any input. Kev

 

[chrishutt]

This boiler has a modulating gas valve, so it's perfectly feasible that the burner would have a low flame for long periods to maintain the flow temperature. It doesn't sound as if anything is necessarily wrong.

The boiler, although old, is an example of solid engineering that you just can't get these days, so worth keeping going, especially if you've splashed out on a new flow switch.

Just make sure that anyone you get in to work on it has a good understanding of how that particular boiler works. Not many will, and those that don't may do more harm than good.

 

[meldrew's_mate]

Sounds like he's got the boiler doing just what it should, heating up quickly on full rate, then modulating down to keep the flow temperature stable. Congratulations to him

The only concern is "is the minimum burner pressure high enough to avoid condensing conditions that lead to rapid corrosion of the flue and heat exchanger?". This is manufacturer's data, if you have, say, 10 or more rads on the system it is likely the boiler will run all day at minimum burner pressure, especially in cold weather.

If you're worried about the gas bills, go and read your meter every day and extrapolate the readings, you'll probably find it's using less gas.

 

[Kevlar13]

Thanks for replies. Sounds ok then.
Just that for years I can remember it firing up with full burner and switching off at regular intervals, now I checked it 6 or 7 times in one day and it was always on low and every other time Ive looked as well. Its in the garage by the way

 

[Agile]

It sounds to me as if your boiler was not modulating to the "low" position before.

This fellow has understood the problems and now the boiler is operating correctly!

The burner has three states, on high, on low and off!

Previously it was either on high or off. Now it has access to all three but correctly spends most of the time on low.

Tony Glazier

 

[Kevlar13]

Thanks, I' ll leave well alone then.
Its 19 years old apparently and this is the first problem. Not bad eh.
I have to admit, I haven't had it serviced in 10 years (I know, I know)

My reasoning is, it would cost more for annual contract with BG than most repairs
Kev