Baxi Solo 2 PF Constantly Ignites - Help Please

[MrJJC]

Hi all,

This is my first post, and apologies in advance if I sound a little stupid on this subject but I really don't know too much about boilers, apart from the basics.

My boiler constantly ignites and cuts out again every couple of minutes when in operation. We don't have any problem getting hot water or heating but surely this can't be right?

We recently moved into our house and the boiler was serviced a few weeks before we moved in. I presumed, perhaps wrongly, that a problem like this would have been picked up. (If of course it was happening then).

Thank you in advance!

 

[gas_man_gaz]

your boiler doesn't modulate the gas pressure so to regulate the temp it has to turn the burner on/off.
wen ya got the heating and water on, does it cycle on and off from the start? or does it only do it wen it gets up to temp?

 

[bobw1956]

Could be the aps dropping out,(yes it would have been picked up at the service, if it was indeed happening then)

 

[MrJJC]

your boiler doesn't modulate the gas pressure so to regulate the temp it has to turn the burner on/off.
wen ya got the heating and water on, does it cycle on and off from the start? or does it only do it wen it gets up to temp?

Er, I am not sure what this really means - I know I probably sound stupid, sorry!

When I turn the water there is no indication the boiler is doing anything but the water is still really hot. And when it gets to temperature it seems to be ok. Does that help answer your question?

 

[misterdubya]

Lets put it simply....

Boiler is cold... then it gets hot.

If will cut out before it gets too hot or it will boil the water inside it - even if you need heat or hot water. Older boilers do that.

When the boilers water has cooled a little it will re-fire (if the hot water or heating is on demand), and cycle will continue until the relevent stats tell it not to.

Your boiler will not fire if you draw off hot water. Forget that idea immediatly as you do not have a combination boiler. Trust us lot on this.

Why does eveyone analyse their boiler before Christmas?

Mr. W.

 

[MrJJC]

Lets put it simply....

Boiler is cold... then it gets hot.

If will cut out before it gets too hot or it will boil the water inside it - even if you need heat or hot water. Older boilers do that.

When the boilers water has cooled a little it will re-fire (if the hot water or heating is on demand), and cycle will continue until the relevent stats tell it not to.

Your boiler will not fire if you draw off hot water. Forget that idea immediatly as you do not have a combination boiler. Trust us lot on this.

Why does eveyone analyse their boiler before Christmas?

Mr. W.

Thanks for the info.

To answer the question then, yes it cycles on and off from the start.

In my defence I haven't analysed my boiler before Christmas like "everyone". I have just moved in to the house.

 

[bobw1956]

Could be the aps dropping out,(yes it would have been picked up at the service, if it was indeed happening then)

 

[MrJJC]

Could be the aps dropping out,(yes it would have been picked up at the service, if it was indeed happening then)

Is this expensive?

 

[misterdubya]

Well, it depends doesn't it?

An aps is not 'expensive'. Nor is the labour to change it. I suggest you get an RGI who is reccomended to you. He / she will ascertain the fault. I cant possibly give advice over a forum as I would need to test components.

Mr. W.

 

[acmedone]

My boiler constantly ignites and cuts out again every couple of minutes when in operation. We don't have any problem getting hot water or heating but surely this can't be right?

I've got one of these and it has always annoyed me to hear it constantly clunking on and off every few seconds. It's very poor design of the electronics. Basically, when it's up to temperature and is putting more heat into the water than can escape, it starts rapid cycling. This is inevitable and not possible to overcome but the design could easily have introduced a longer cooling period to reduce the frequency. It already has a 2 minute pump delay, so why they couldn't have held off the next burn for that period as well...

 

[MrJJC]

OK, thanks guys.

I guess now I will have to go and find a local engineer to correct this.

 

[Agile]

This is inevitable and not possible to overcome but the design could easily have introduced a longer cooling period to reduce the frequency. It already has a 2 minute pump delay, so why they couldn't have held off the next burn for that period as well...

If the boiler size is correctly matched to the load then it will not need to cycle very much.

This is done by the installer by choosing the model which matches the load.

Fine adjustment is by range rating the boiler and this gives about 20% variation. This would normally be checked during the annual service.

Over sizing boilers results in excessive cycling and less efficiency.

Tony Glazier

 

[stem]

My boiler constantly ignites and cuts out again every couple of minutes when in operation. We don't have any problem getting hot water or heating but surely this can't be right?

Afraid so, it's the old technology. I've got a Baxi Solo also which is 12 years old and has always worked like this. When the heating is first switched on it runs constantly, then as the system starts to heat up, the boiler starts to have short off periods every now and again. The longer the system is run for, the 'off' periods gradually increase and the 'on' periods get shorter. It normally ends up with the burner running for about a minute and then having a minute off before lighting up again.

It's the Solo's way of keeping the temperature of the water leaving the boiler at a constant temperature, as set on the boiler thermostat.

The same thing happens when it's heating the hot water too.

 

[acmedone]

If the boiler size is correctly matched to the load then it will not need to cycle very much.

The load can vary between all radiators plus hot water cylinder, to some radiators with others turned off by thermostatic taps, to the water cylinder on its own. On top of that, a high output is needed for a quick response, then when temperature is established, a low level to maintain it.

Impossible to "match" a boiler to such variability. It is the responsibility of the boiler designer to make the boiler cope. Even with the electronics techniques used (*), better cycle control should have been a trivial design issue.

(*) It uses components available since the late 70s. When I bought my Solo in 94, microprocessors were already well established. A board with a micro would have been much cheaper. It would be interesting to know when the design actually took place.

The other design issue with Solo is that the water temperature sensor is in the output side. It should be in the input side so that when the burners switch off, the sensor doesn't see a large temperature drop. There is still a separate cut out to protect the thing, after all.

This is done by the installer by choosing the model which matches the load.

I have the 15kW model (which, I think, was the lowest rating available) in a 4 bed detached. Most of the year it is only heating the cylinder and for the best part of a typical winter only 2 radiators are normally active. Difficult to see how the installation could have been bettered.

 

[Agile]

The other design issue with Solo is that the water temperature sensor is in the output side. It should be in the input side so that when the burners switch off, the sensor doesn't see a large temperature drop. There is still a separate cut out to protect the thing, after all.

I have the 15kW model (which, I think, was the lowest rating available) in a 4 bed detached. Most of the year it is only heating the cylinder and for the best part of a typical winter only 2 radiators are normally active. Difficult to see how the installation could have been bettered.

I am afraid that you dont know much about boiler design!

The single sensor has to be on the output so that the boiler is controlled to a set OUTPUT temperature! That set temperature is what the user can use to control the heat output from the rads.

The boiler should be chosen and set to match the maximum heating load plus 2 kW for hot water. It then has to cycle to match the heat output required at any particular time. A well insulated four bed detached house will need about 15 kW so your boiler is about right.

In spite of what you think, the Baxi Solo 2 was also made in 12 kW and 9 kW models.

Its a pretty basic design and like all boilers rather uses older design concepts on its control circuitry. But that made them more reliable.

Micro processors only became common on boiler PCBs since about the year 2000. Even now most PCBs still use mechanical relays instead of triacs or solid state relays. Probably because they are still cheaper but possibly because they are thought less likely to stick on when controlling the gas valve.

Tony