Vokera Linea 735 Intermittent Heating

[abeach]

I have a Vokera Linea 735 combi boiler powering my central heating and hot water. When starting from cold (hard reset, power off) the heating fires up nicely following a demand for heat from the time clock (no additional controls). Following a number of hot water requests the heating stops working, the pump is running but the burner is never ignited for the heating. The only burner ignition that occurs is for hot water or pre-heat. The pump will continue to be run until the demand for heat is removed (time clock off), resulting in very cold radiators (boiler reporting temperatures such as 22 Dec C on the heating loop).

If a soft reset is performed (switch to the off position) when the switch is returned to the "heating and hot water" position the heating continues to be inhibited. The only way to get the heating back is to remove the power from the boiler. Once this hard reset is applied the heating works as normal again until it gets itself stuck in the heating inhibit mode after a few hot water requests.

Does anyone have any ideas?

 

[nickso]

I would be guessing the Anti-cycle delay is faulty, expensive guess though, you might want to get a fixed price repair from one of the larger companies. Might also want to check the primary thermistor.

The On/Off switch on a linea actually does very little in the way of switching it off as such, many functions stay energised, the pre-heat does, and the ACD may be one of them.

 

[abeach]

Do you not think it could possibly be the divertor valve or its actutator getting stuck in hw mode? The removing of power could reset the valve/actutator giving heating again?

 

[Agile]

If either the DHW demand is stuck on OR a valve has stuck in a DHW position when CH is required then the boiler will cycle on for a few seconds every 15-30 min to keep itself warm.

From what you say this does not happen and that would point me to a failed anticycle circuit.

Tony

 

[abeach]

Sorry, it does fire for a very short period, say 5s every 10-15m. I thought this was the hw pre-heat. Immediately after this the temperature lcd falls back sharply from 60+ to a low temp. Thanks for your assistance

 

[Agile]

It still could be the DHW preheat.

> Hot Water Preheat Function

> To disable remove jumper JP6
> To enable add jumper JP6

Accessing the PCB should only be done if you are competent to work on circuitry safely.

Tony

 

[abeach]

So if I disable the pre-heat with jumper 6 and it still cycles on every 15-30 mins for a short period, the chances are it is a stuck valve? If not it might be this anti-cycle thing?

 

[Agile]

A stuck valve would need to be intermittent.

Your description sems to imply that its pretty consistent. Is it really?

Unfortunately, with boiler repairs you cannot just guess at a possible cause. You need to test everything to be sure.

Unless you just want to blindly change parts as so many do!

Tony

 

[abeach]

Ok, understood.

It is intermittent in the fact that it doesn't necessarily happen on the first use of DHW. For example this morning, the shower and another DHW outlet (used for >20s) were used and it was still heating ok. However, last night after a couple of short uses of DHW it got stuck in this faulty mode I have described. However, it is consistent in the fact that to get heating back again you have to remove mains from the boiler.

Before Christmas I had a day when the boiler was reporting error code "01" failure to ignite. However, it was not going through the ignition sequence, just straight from the switch off position to red flashing LED and 01 on the LCD. This seemed to clear after a hard reset (mains off) and it has not done it since. May be that instance was the start of intermittent electronic problems, that the new fault condition is just one of?

Being an engineer (not gas) my self I was just trying to see if it was likely to be a dodgy valve or actuator that would have been a relatively cheap and simple fix (< £40 parts) rather than a long protracted hundreds of pounds of a job.

 

[Agile]

It certainly does sound like a PCB problem.

I would expect they are about £135 and an engineer might charge perhaps £90 to fit and test the boiler.

A British Gas fixed price repair MIGHT be a viable alternative.

Tony

 

[nickso]

Easy to see if it's stuck in DHW. When it's faulty test for continuity across the DHW flow switch. You usually get a lot of overheating noise when they do that though.

The diverter motor can be tested easily by removing it. Diverter pin out is CH mode. Look at the motor when you take it off, if you can't move the brass bit back inside it then it's still in DHW mode.

Still think it's the PCB but I'll cover my arse and say its 'cos I'm not looking at it.

 

[abeach]

Well it has gone back to working fine at the moment no matter if I use the DHW or not. So I am not going to touch it for now. Deffo sounds PCBish now though.

 

[Thagun]

I removed the jumper JP6 to disable the pre-heat.

Problem solved.

I think after using the DHW it was going to DHW pre-heat and getting stuck.

 

[ianmcd]

a six year old post and you come up with that ?????

 

[Thagun]

Actually not fixed.

Thought it was but it's back to being weird.

Plus, although it's a six year old thread it's a new problem for me.

Reckon pcb it is now