Is my boiler underpowered?

[amudda]

Hi all,

Have moved into a new house, and the current cold weather has highlighted the inadequacies of the current heating system.....

Not all my rads are getting hot. By turning off the hot rads, I can get each one to heat up by itself, so I don't think it's sludge - I just can't get them all hot at the same time, no matter how I try and balance the system.

Could my boiler be underpowered? And if it is, is rads not getting hot a symptom of an underpowered boiler? My theory is as follows, and I'd appreciate comments from someone who understands more about heating than me!

It's a large-ish house, 5 bedroom, 2 bathroom, and has been extended over time. I have an Ideal Minimiser SE80, about 10 years old, which the manual says is rated at about 23kW.

I have 14 radiators in my house, with a total surface area of 18.43 square metres. Looking in the FAQ on this site, it says that 0.6 square metres equates to about 1kW - so, by that calculation, I need about a 30kW boiler to heat my rads, plus, say 2kW for hot water = 32kW. Therefore, at 23kW (assuming that, at 10 years old, it can still produce even that) my boiler is seriously underpowered, and therefore I'm never going to be able to get all my rads hot at the same time, because the boiler just can't pump out the right amount of heat. Which means it's time for a new boiler.

Does that sound right? Any opinons welcome!

 

[collyplumb]

Hi, I am not a regular on here so the others may come back with something better but..

Have you tried balancing the system? This means turning the lockshield valves of the radiators that are getting hot down to create resistance (not the Thermostatic Rad Valves) thus causing the pump to push the water to further points in the system. Don't turn them all the way off but .5 to 1 turn from off should work. This will take some time to be perfect. A good way to check if this is part of the problem is feeling the return central heating pipe at the boiler to feel if it is hot before the rads are hot.

 

[collyplumb]

Sounds like you have already tried to balance the system... I will read the posts better next time.

 

[Diyisfun]

COLLYPLUMB..He has said he has tried to balance the system.

How many rads do you have & sizes approx also single or double.

Property type, ie Deatached, semi & location

I dont know the spec of the boiler, but the experts on here will do quick calcs for you.
Although if the house has been extended since the boiler was installed, I would guess its under powered.

 

[D_Hailsham]

Not all my rads are getting hot. By turning off the hot rads, I can get each one to heat up by itself, so I don't think it's sludge - I just can't get them all hot at the same time, no matter how I try and balance the system.

The system is not properly balanced. When it is, all radiators will feel equally warm to the touch. If your boiler is underpowered for the rads you may not be able to achieve the stated output from the rads, i.e the flow and return temperatures will be lower, but there should not be any significant difference between rad temperatures.

It's a large-ish house, 5 bedroom, 2 bathroom, and has been extended over time. I have an Ideal Minimiser SE80, about 10 years old, which the manual says is rated at about 23kW.

Use either of these calculators to find out what size boiler you need. They should give virtually identical results.

Sedbuk Boiler Calculator

EST online boiler calculator

I have 14 radiators in my house, with a total surface area of 18.43 square metres. Looking in the FAQ on this site, it says that 0.6 square metres equates to about 1kW - so, by that calculation, I need about a 30kW boiler to heat my rads, plus, say 2kW for hot water = 32kW. Therefore, at 23kW (assuming that, at 10 years old, it can still pro

A better way of estimating rad output is to use a manufacturer's catalogue such as the Stelrad Elite Catalogue. It only covers standard rads, not designer ones.

The boiler size is the important thing. Your rads need to be about 15-20% larger than the boiler. Any smaller and the house may not get up to temperature. Larger is OK, it just means the boiler and rads will run at a lower temperature.

Your boiler is Sedbuk Band B.

 

[Diyisfun]

Sounds like you have already tried to balance the system... I will read the posts better next time.

Well spotted..

 

[amudda]

The system is not properly balanced. When it is, all radiators will feel equally warm to the touch. If your boiler is underpowered for the rads you may not be able to achieve the stated output from the rads, i.e the flow and return temperatures will be lower, but there should not be any significant difference between rad temperatures.

Ah, i see what you mean - if my system was properly balanced, all radiators would be the same temperature, even if that temperature was too cold because the boiler was underpowered. So I need to go back to balancing again and try to get that right.

The calculator reckons I need a 32kW boiler - but it reduces that to a 24kW boiler if I replace my rubbish single glazing with double, and properly insulate the roof, both of which I am having done this year. So maybe I should try harder to balance the system properly, get the windows and insulation done, and then see what the situation is like, rather than jumping in to replace the boiler immediately

When you say the rads need to be 15% - 20% larger than the boiler, do you mean that the total output of the radiators should be higher than the heat output of the boiler? i.e. if my rads can output 32kW, I should look at a 28kW boiler, not a 32kW one?

Diyisfun, my house is detached and located on the Wirral (North West, near the sea) I have 14 rads as follows :

0.7m x 1m double
0.8m x 0.5m single
0.8m x 0.6m double
0.3m x 1.4m double
1m x 0.6m double
1.6m x 0.6m double
2.1m x 0.5m double
1.8m x 0.45m double
1.6m x 0.5m double
1.3m x 0.45m double
1.4m x 0.5m single
1m x 0.45m single
2.3m x 0.45m double
2.3m x 0.45m double

(this is where I got my 18.43 square metres) It's an open vented system. For those radiators, and given that the whole house sizing calculators reckon I need 24kW once I've done my glazing and insulation - does a 24kW boiler sound OK, or would you be tempted to put something a bit bigger in? (as the boilers 10 years old, it's gonna need replacing sooner or later...)

 

[BingoBongo]

The system is not properly balanced. When it is, all radiators will feel equally warm to the touch. If your boiler is underpowered for the rads you may not be able to achieve the stated output from the rads, i.e the flow and return temperatures will be lower, but there should not be any significant difference between rad temperatures.

Ah, i see what you mean - if my system was properly balanced, all radiators would be the same temperature, even if that temperature was too cold because the boiler was underpowered. So I need to go back to balancing again and try to get that right.

The calculator reckons I need a 32kW boiler - but it reduces that to a 24kW boiler if I replace my rubbish single glazing with double, and properly insulate the roof, both of which I am having done this year. So maybe I should try harder to balance the system properly, get the windows and insulation done, and then see what the situation is like, rather than jumping in to replace the boiler immediately

When you say the rads need to be 15% - 20% larger than the boiler, do you mean that the total output of the radiators should be higher than the heat output of the boiler? i.e. if my rads can output 32kW, I should look at a 28kW boiler, not a 32kW one?

Diyisfun, my house is detached and located on the Wirral (North West, near the sea) I have 14 rads as follows :

0.7m x 1m double
0.8m x 0.5m single
0.8m x 0.6m double
0.3m x 1.4m double
1m x 0.6m double
1.6m x 0.6m double
2.1m x 0.5m double
1.8m x 0.45m double
1.6m x 0.5m double
1.3m x 0.45m double
1.4m x 0.5m single
1m x 0.45m single
2.3m x 0.45m double
2.3m x 0.45m double

(this is where I got my 18.43 square metres) It's an open vented system. For those radiators, and given that the whole house sizing calculators reckon I need 24kW once I've done my glazing and insulation - does a 24kW boiler sound OK, or would you be tempted to put something a bit bigger in? (as the boilers 10 years old, it's gonna need replacing sooner or later...)

dont put a 24kw boiler near those size of rads.

what is your hot water usage?

 

[amudda]

For hot water, we tend to heat up a tank in the morning (for an hour) and in the evening (for an hour) and that's enough for us.

 

[D_Hailsham]

Ah, i see what you mean - if my system was properly balanced, all radiators would be the same temperature, even if that temperature was too cold because the boiler was underpowered. So I need to go back to balancing again and try to get that right.

You've got it!

The calculator reckons I need a 32kW boiler - but it reduces that to a 24kW boiler if I replace my rubbish single glazing with double, and properly insulate the roof, both of which I am having done this year. So maybe I should try harder to balance the system properly, get the windows and insulation done, and then see what the situation is like, rather than jumping in to replace the boiler immediately

That's a sensible approach. Did you know there are many special offers and grants for insulation? Check out Energy Savings Trust Grant Search.

When you say the rads need to be 15% - 20% larger than the boiler, do you mean that the total output of the radiators should be higher than the heat output of the boiler? i.e. if my rads can output 32kW, I should look at a 28kW boiler, not a 32kW one?

No it's the other way round! If the calculator says you need a 24kW boiler (22kW heat, 2kW water) then you need 25-26kW of radiators, more is OK.

The rad size info is interesting, but turning it into KW using the Stelrad data would be more useful.

 

[DarrenGuest]

Have you got a manual bypass valve fitted by the pump? If so check that it is not open too much. If you close it fully do the rads all get hot?

It should be open a little, much better to just replace it with an automatic bypass valve.

I thought our heating was poor for 3 years, had loads of heating engineers fiddle with it and try to sell me £800 powerflushes. After doing my own research and fitting a new Grundfos pump and an automatic bypass valve the heating is now perfect. I was getting so frustrated with it we were considering having the whole heating system replaced.

 

[Axel]

Had the same problem last week - the customer's 'heating engineer had decided that the pipe sizing etc was not sufficient and they would have to live with it. I am not an expert, but they called me along and all I had to do was close the 22mm bypass valve until nearly closed, and their rads started heating up like never before. £ 30 was cheap for them and an easy earner for me!

 

[amudda]

Thanks for the advice all - much appreciated!

Have gone back to balancing, so will see where that gets me over the next few days. I'll also convert the rad sizes to kW using the Stelrad catalogue and post back the results.

I did have a look at the Manual Bypass - it's a 22mm pipe, and the valve was about 1/3 of a turn open open - I've closed it down a little, so it's now just under 1/4 of a turn open - hasn't made much difference, but every little helps!

Could my pump be wearing out/underpowered? Would that cause the rads to not heat up properly - ie only get hot at the top? It's a Myson Compact CP63 - should that be suitable? It isn't making any strange noises, so I've no reason to think it's bust - just want to know if it could be a potential culprit.

 

[jono_h]

I've just looked at a similar problem at my brothers house. Some rads were getting hot others only warm, with the hot rads swapping between rooms.
It appears that the cylinder thermostat was faulty and wasn't closing the 3 port valve. This meant that the water from the boiler was always flowing through the hot cylinder, and with water taking the path of least resistance very little was flowing through the rads.
A new cylinder stat seems to have cured the problem.

 

[DarrenGuest]

If the Bypass valve is only open 1/3 of a turn then it won't be that causing the problem. If the rads are hot at the top but cold at the bottom it suggests to me that they are not getting enough flow and the system is not balanced properly. After you have balanced the radiators which ones are still not getting hot, the ones furthest of closest to the boiler?

If you want to eliminate sludge from the equation you could always hire a powerflushing machine and have a go yourself if you are confident.

Going back to the pump, what speed is it on and does it make any difference if you increase the speed?