Vokera Line 24, now useless at heating water

[AlWilliams]

We've got a Linea 24, it was here when we bought the house and has never been that great at giving hot water.

Over the last couple of months, it's got a lot worse. When a hot tap is opened the boiler fires, the water temp climbs then when it gets to about 40 deg the burners shut down. It stays that way till the temp gets to around 30 deg then repeats. All the while making lot of shhing noises.

This make showering a bit like doing the hoky pokey and is no good for washing up.

It's been looked at, but the chap didn't really know and suggested working through a number of options, which before long could total quite a bill and it would nearly be cheaper to buy a new boiler, something we can't stretch to.

I've read through a number of threads on this site, the DHW seems like a common culprit, but as our water temp never rockets to 90+ when the tap is open I'm not sure.

Any advice gratefully received.
Thanks.

 

[twgas]

let the rads go cold then try the hot water, does the flow pipe (2nd from left) heat up?

 

[DP]

Your complaint is not with the boiler but quality of water in the system. NO modern boiler will operate as designed if system water is 'dirty'

If the diverter was passing to rads during HW mode, burner would not go out.

 

[twgas]

Your complaint is not with the boiler but quality of water in the system. NO modern boiler will operate as designed if system water is 'dirty'

If the diverter was passing to rads during HW mode, burner would not go out.

good point

 

[AlWilliams]

No, I think that pipe stays cold but will check later this evening when we don't need the heating (which works well).

The system water is clean, as it's been drained and refilled a couple of times over the past year due to new radiators being fitted. Inhibitor added each time.

 

[DP]

The system water is clean, as it's been drained and refilled a couple of times over the past year due to new radiators being fitted. Inhibitor added each time

Are you sure? Select CH, run the boiler to heat radiators. Now run a hot tap. When the display reaches 30 and burner pops, flip the valve on the right hand pipe from 12 o'clock position to 9 o'clock position and see what the digi display indicates. If it is high 80, even 90, then it is dirt in the HW heat exchanger.

Draining a system does not remove muck and dirt/ sediment from the system. If you do not believe me, remove a radiator and tip one end up drain the sediment at the base of the radiator.

Attended a Linea today. I have never seen a boiler guts so clean on a boiler. The diverter spring was silver, the manifold had no black deposits in it- yellow brass even where water in contact.

 

[AlWilliams]

Thanks All,

DP, hope I got this right. I ran the CH and opened the tap, on reaching the lowest temp, as the boiler re lit I closed the brass valve on the RH CH pipe. The burner shut down when approximately 40 deg was reached.

So no change from previous symptoms.

 

[nickso]

The supposed foolproof test for the DHW H/E is not foolproof at all IMO and I never use it. Far better to actually test the temps of the water entering the DHW H/e on both sides and make your judgement from that. Assuming the Gas valve settings are correct there's a good chance its choked.

If it is noisy on Hot water its almost a given at least one H/E is choked. Is it noisy on CH too? If so they are both dirty.

You will never know unless it's tested properly.

 

[DP]

Try doing what I ask when

The burner shut down when approximately 40 deg was reached.

Burner shuts down when things are getting TOO HOT for the boiler

 

[AlWilliams]

Try doing what I ask when

The burner shut down when approximately 40 deg was reached.

Burner shuts down when things are getting TOO HOT for the boiler

That's whats me confused, the burners definately shut down as 40 deg is reached when running HW but it will happily tick over at 70 plus degrees when just running CH.

 

[DP]

OP, can you carry out the test suggested and report back please? In CH mode ALL the heat is transferred to load. THAT is NOT the case during HW mode with your installation. Burner is shutting down else water be turned to steam

 

[AlWilliams]

Thanks again.
Regarding the test, if its nickso's suggestion, I don't have any way of measuring the temp differential between the dhw exchange inlet and outlet unfortunately.
If you mean the test you suggested DP, sorry I must have misinterpreted your instructions as I thought I'd carried it out correctly. edit - Ah, you mean the cold inlet DP, not the RH CH pipe, will check later this afternoon.

Having thought about it quite a bit last night, I'm starting to think the problem is a combination of faults. Perhaps a control one and a plumbing one.

 

[DP]

Fault fnding is a logical process. Thinking outside the box equates to replacing components that might not be defective.

 

[AlWilliams]

Ok, i've got somewhere at last.

I opened a hot tap and turned off the RH valve as the boiler relit at 30 odd degrees, the temp reading climbed fairly steadily till approx 85 deg where it seemed to level out. The burners we still going at this point. I then opened the RH valve and the burner shut off pretty much immediately. Temperature fell to 30 ish and be boiler then cycled to 40 deg and down again, as before.

So, getting the DHW exchanger cleaned or replaced is the starting point?

Thanks for your help.

 

[Agile]

Fault fnding is a logical process. Thinking outside the box equates to replacing components that might not be defective.

I thought that you DID sometimes have to think outside the box to diagnose unusual faults.

It must be difficult to diagnose boiler faults if you cannot measure pipe temperatures!

Tony