Another Viessmann 100 problem

[MikeAustin]

The F4 indication does not unequivocally point to the spark generator.

If the spark gen is breaking down Viessmann will usually fix it under warranty. It does not cause a 45C problem in our experience, but the new unit has better shielding because the old one used to affect the PCB in some strange ways. Because of this it took Viessmann a fair few months to find the problem when it first started knocking ut boilers with F4.

So I would start with this.

If you had a blockage, you would expect the boiler to get to 75C very quickly and then shut down.

I am really grateful to all you guys for your help on this!

The installer started with replacing the F/R thermistors under direction from Viessmann. Then all the radiator valves were replaced, the sytem was power-flushed and re-filled (I noted no special procedure filling the boiler). Then the circuit board was replaced under direction from Viessmann. It now seems to me that they should have started with the grey ignition unit. This must be the only thing left to address as the condensate drain looks clear to me.

Regarding the blockage, what you say would make sense to me. However, I understand there are flow sensors as well as thermistors and that a blockage would be detected by reading these before the boiler temperature peaks out.

My plan of action now (as it took the installer 2 weeks to get the new circuit board in) is to drive to Viessmann in Telford this afternoon and get a new black ignition unit. That is over 2 hours away from Bristol. Dammit, I might even put the new ignition unit in myself!

 

[Agile]

Is this boiler still under warrantee?

Are Viessmann giving you the new PCB and sensors ( which are thermistors! ) free or are you paying for them?

Before driving to Telford make sure you have arranged it with them and have a NAME to ask for when you arrive!

An easier solution would be to ask for your area sales rep as they have a stock of black ones and you may have a rep in Bristol.

Tony

 

[MikeAustin]

Is this boiler still under warrantee?

Are Viessmann giving you the new PCB and sensors ( which are thermistors! ) free or are you paying for them?

Before driving to Telford make sure you have arranged it with them and have a NAME to ask for when you arrive!

An easier solution would be to ask for your area sales rep as they have a stock of black ones and you may have a rep in Bristol.

Tony

It was fitted in November 2005. I thought the warrantee was 3 years, but apparently it is 2 years. The installer has tried to get the parts free from Viessmann but they would not do it. He has paid for the thermistors/sensors himself but I have to pay £180+ for the PCB. Given that these PCBs can also be a problem, maybe a new one is a good idea anyway.

I have arranged to collect the black ignition unit and also the electrodes (just in case) from Telford this afternoon - £31 total.

 

[Agile]

Over 95% of the F4 faults are grey ignition and thats well worth changing on sped.

The much more expensive PCB rarely fails.

Having said that there was a batch of faulty PCB on one of the Viessmann models about 2005/6 and they were all going to be changed under warrantee at the time ( when the boiler had been registered ).

Tony

 

[MikeAustin]

Over 95% of the F4 faults are grey ignition and thats well worth changing on sped.

The much more expensive PCB rarely fails.

Having said that there was a batch of faulty PCB on one of the Viessmann models about 2005/6 and they were all going to be changed under warrantee at the time ( when the boiler had been registered ).

Tony

Well, I have now replaced the ignition unit - and the electrode for good measure. It now fires up again and the F4 problem has gone. However, I am now back with my original problem of the boiler cutting in and out.

 

[MikeAustin]

I am now back with my original problem of the boiler cutting in and out.

How about low gas supply pressure? Would that cause this behaviour? The installer said maybe there is some obstruction in the boiler itself. I am a bit sceptical of this.

 

[JohnD]

mine used to cut out due to insufficient flow, meaning there was not enough load on the boiler. This happened when it was on HW only, as the cyl supply is necked down to 15mm and I have a Alpha+ pump

My remedy was to turn up the pump speed a bit.

There might be a cleverer way., I am just a householder.



*edited to say that the low flow was when it was on Hot Water only

 

[Agile]

How about low gas supply pressure? Would that cause this behaviour?

The installer said maybe there is some obstruction in the boiler itself. I am a bit sceptical of this.

He meant in the heating flow NOT the gas supply.

He is meant to have correctly have sized the gas pipes and to have measured the supply pressures at full load to ensure they meet requirements.

Its not normally possible for the householder to know more than the installer!

I know that they are all plumbers, who as we all know, left school at 15 are are very thick!

But that might not really reflect the situation!

Tony

 

[MikeAustin]

How about low gas supply pressure? Would that cause this behaviour?

The installer said maybe there is some obstruction in the boiler itself. I am a bit sceptical of this.

He meant in the heating flow NOT the gas supply.

Yes, I know. They were separate points I was making.

He is meant to have correctly have sized the gas pipes and to have measured the supply pressures at full load to ensure they meet requirements.

It was running OK for 3 years. I wondered if there may be fluctuations in gas pressure. As you can see, I am really stumped for causes of this problem now - and I am not too keen on the idea of the installer taking the boiler apart!

 

[JohnD]

if (as I think possible) it is caused by insufficient water flow through the boiler, how do you know the pump is working correctly, you have enough flow through rads and cylinder, and you do not have sludge, sediment or air in the pipes?

Is your system open vented or sealed? If open, is there mud in the F&E? What happens when you bleed the rads? Is the water black? Was the boiler fitted to an existing dirty system?

I am still a householder.

 

[MikeAustin]

if (as I think possible) it is caused by insufficient water flow through the boiler, how do you know the pump is working correctly, you have enough flow through rads and cylinder, and you do not have sludge, sediment or air in the pipes?

Is your system open vented or sealed? If open, is there mud in the F&E? What happens when you bleed the rads? Is the water black? Was the boiler fitted to an existing dirty system?

I am still a householder.

I think there is sufficient flow. For example, with the heating alone and the boiler switching on and off, the flow is warm and the return is cold. With the hot water on - and having had the immersion heater on for a while - the return becomes warm. I can feel the flow through the radiators by holding the pipe that leads to them. Also, a new more powerful pump was fitted temporarily a few weeks ago but the problem remained.

The system was power flushed a few weeks ago and a Magnaclean added. Four days ago, I took out the filter. It was a bit black but not bad. I washed it and put it back. When I bleed the rads the water is very clean. The boiler was fitted over three years ago, and it has been working OK until December or so, when it gradually became sluggish. I don't recall a power flush being done when it was installed, though.

I haven't checked the F&E (I presume that means "fill and expansion" tank?) as it seems everything is clean throughout the system elsewhere.

 

[Agile]

I think there is sufficient flow. For example, with the heating alone and the boiler switching on and off, the flow is warm and the return is cold.

That is EXACTLY what happens when there is insufficient flow!

The differential temperature across the boiler should be about 15-20°C and if its more that that then the flow is too small.

Tony

 

[MikeAustin]

I think there is sufficient flow. For example, with the heating alone and the boiler switching on and off, the flow is warm and the return is cold.

That is EXACTLY what happens when there is insufficient flow!

The differential temperature across the boiler should be about 15-20°C and if its more that that then the flow is too small.

Tony

Yes, normally. But I am talking about a boiler that comes on for a few seconds and trips off at maybe 40 degrees initially. This small amount of heat (mass*temperature) is immediately dissipated in the radiators. If you read later in my post, the pump can return water heated by the cylinder. That should indicate there is enough flow. (This would be a novel way to heat the house!)

 

[Agile]

You seem to be missing the point.

The boiler does not know where its water is going!

How can you explain how the boiler could give a flow temperature of 40°C if its return is say 20° if there really was sufficient flow?

The mere fact that it works normally on hot water just means that the flow is adequate on hot water only.

Why dont you measure the flow and return temperatures on hot water and then on heating?

Tony

 

[MikeAustin]

You seem to be missing the point.

The boiler does not know where its water is going!

I am certainly missing something here! I don't think I implied that the boiler should know where its water is going. In principle, the flow could go down the drain as long as an equal amount of water were to be fed into the return.

How can you explain how the boiler could give a flow temperature of 40°C if its return is say 20° if there really was sufficient flow?

Perhaps I have misunderstood. I thought that the boiler should reach maximum temperature and only cut when the return is within range of this. Am I wrong about this? At the moment it is very, very slowly (several hours) inching its way up to working temperature.

The mere fact that it works normally on hot water just means that the flow is adequate on hot water only.

Yes, this is true. But doesn't it prove the pump is OK - at least for F&R to the cylinder?

Why dont you measure the flow and return temperatures on hot water and then on heating?

The only numerical measure I have is on the display. Otherwise, it is 'hands on' judgement. The problem of reaching the operating temperature is on either heating or hot water or both. It doesn't seem to matter if warm water is returned from a tank heated by an immersion heater.