Is this an Oversized boiler?

[Dan Stokes]

hi all,
First post, mostly been lurking about.

I have an issue with my Baxi Solo pfl 50 short cycling. It runs fine for about 45 mins when system starts from cold then starts cycling on its stat about 5 mins on then 5 mins off. I’ve checked flow and return temps from boiler and shows it’s definately cycling on the stat. It does this until the hallway stat is satisfied. I’ve checked radiator balancing and tried pump speeds but doesn’t seem to help. Just added up the radiators outputs at 26000 btus, with this in mind would you expect to see that kind of cycling with a 50000 btu boiler? Cheers

 

[ShaunCorbs]

Baxi solos are old has it just started doing this ?

 

[Dan Stokes]

It’s 15 years old I think. I’m not sure if it’s always been like this

 

[Last Plumber]

hi all,
First post, mostly been lurking about.

I have an issue with my Baxi Solo pfl 50 short cycling. It runs fine for about 45 mins when system starts from cold then starts cycling on its stat about 5 mins on then 5 mins off. I’ve checked flow and return temps from boiler and shows it’s definately cycling on the stat. It does this until the hallway stat is satisfied. I’ve checked radiator balancing and tried pump speeds but doesn’t seem to help. Just added up the radiators outputs at 26000 btus, with this in mind would you expect to see that kind of cycling with a 50000 btu boiler? Cheers

Boiler may be over sized for the system, it has probably always done that.
Have you calculated the Heat requirements for the property?
What size of Domestic Hot water Cylinder do you have?

 

[Dan Stokes]

I did have a look on the net about heat requirements but couldn’t find anything that useful, it’s a 15 yr old townhouse with three beds and 9 rads in total. The cylinder is an rm cylinder 120l. The boiler fan (I think) is a bit noisey and I think that’s the reason I have noticed the short cycling. Basically I’m thinking either spend x amount on getting the boiler fan replaced and boiler serviced or replacing completely for something modulating that’s going to save probably quite a bit of money esp if this short cycling is due to it being oversized

 

[fixitflav]

I did have a look on the net about heat requirements but couldn’t find anything that useful, it’s a 15 yr old townhouse with three beds and 9 rads in total. The cylinder is an rm cylinder 120l. The boiler fan (I think) is a bit noisey and I think that’s the reason I have noticed the short cycling. Basically I’m thinking either spend x amount on getting the boiler fan replaced and boiler serviced or replacing completely for something modulating that’s going to save probably quite a bit of money esp if this short cycling is due to it being oversized

As demand is 26000BTUand boiler output is 50000, equal times on and off is about what you'd expect. Is it a problem?
I'm not sure on/off operation in itself is much less efficient than modulating, but a new boiler would be more efficient for a number of reasons. However, it would take a good many years to recover the cost.

 

[Dan Stokes]

so the short cycling is to be expected ? It’s not really an issue for me, house gets hot enough. I’m thinking about efficiency and these cycles taking a toll on the boilers components

 

[dan_the_plumber]

Try turning hot water function on less often. That way the cylinder will cool as you use the hot water.
Then you’ll be able to dump a load of heat energy into the cylinder during peak use and the boiler will cycle less often

 

[Dan Stokes]

Try turning hot water function on less often. That way the cylinder will cool as you use the hot water.
Then you’ll be able to dump a load of heat energy into the cylinder during peak use and the boiler will cycle less often

Good shout dan cheers

 

[dan_the_plumber]

Good shout dan cheers

Also if you set flow temp on boiler to match required temp on cylinder stat (65 degrees) that will reduce cycling too.