Radiators not hot enough

[newbiev]

I have recently moved into a new home and replaced some of the radiators. A couple of them are larger double panels compared to what they originally were. In total, 3 large type 21's, 2 large type 22's and 2 small ones.
It is a regular vented system with a cylinder and tank in loft.

Now it seems the radiators do not get hot enough. They are hot, but compared to where I used to live, the radiators used to get too hot to touch, where as I can touch the new ones comfortably. As a result the rooms takes forever to warm up, and never really reaches the desired temp of 20-21c.

So the most obvious cause to my untrained mind would be the boiler doesn't pack enough power to deal with the new rads. It is an old boiler, possibly 15-20 years old.

But could it be something that could be a quick fix in the short term?
I have bled all the rads, and do so regularly.
I have turned the pump up from 2 to 3. This has helped slightly, but not enough.

Given the cost of moving home etc, I don't really want to replace the boiler right away, so if anyone has any alternative suggestions on how to improve the situation, I would be grateful.

Thanks

 

[John D v2.0]

Is the boiler firing constantly on maximum power or is it modulating down?
If the former then it's not powerful enough, if the latter the water is moving too slowly.
How hot are the flow and return from all the rads? Maybe the system needs balancing again to have a bigger flow through the new rads.

 

[alan333]

Check the temp setting on the boiler isn't at low.

 

[newbiev]

Is the boiler firing constantly on maximum power or is it modulating down?
If the former then it's not powerful enough, if the latter the water is moving too slowly.
How hot are the flow and return from all the rads? Maybe the system needs balancing again to have a bigger flow through the new rads.

It's not firing constantly. It keeps going on and off. So this would mean the water is moving too slowly?

Would this indicate I need to change the pump?

 

[John D v2.0]

Yes, check the valves are open enough (balancing) and the pump is on the highest settings. Could be muck in the system, what did the water look like?

 

[newbiev]

Yes, check the valves are open enough (balancing) and the pump is on the highest settings. Could be muck in the system, what did the water look like?

Will give this a try, thanks. The water looks fairly clear, although black in one of the small rads that wasn't changed.

 

[JohnD]

Are ANY of the radiators hot?

What colour is the hot water cylinder? Is that hot?

Feel the "return" pipe on the boiler. Is it hot?

 

[JohnD]

Check the temp setting on the boiler isn't at low.

have you done that?

 

[newbiev]

have you done that?

Boiler setting is high.

All the radiators are hot, just not very hot. I will check the return pipe. Should this be hot hot?

Hot water cylinder is copper, that again is hot, but not very hot.

 

[JohnD]

the return pipe should be slightly cooler than all your radiators. If it is hotter, then the flow is bypassing them.

If any of your radiators are hotter than the others, they are stealing the flow due to poor balancing.

 

[newbiev]

the return pipe should be slightly cooler than all your radiators. If it is hotter, then the flow is bypassing them.

If any of your radiators are hotter than the others, they are stealing the flow due to poor balancing.

Thanks, I will check this out

 

[stem]

How are the radiators piped up? Most use the 'two pipe' system, but what you describe would be normal for the older 'one pipe' systems, especially the radiators towards the end of the loop.

 

[newbiev]

How are the radiators piped up? Most use the 'two pipe' system, but what you describe would be normal for the older 'one pipe' systems, especially the radiators towards the end of the loop.

View attachment 137500

I've never thought of this, but will take a look under the floor boards and see what I find.
Is there a significant disadvantage of having one pipe?

 

[stem]

Only that the radiators don't get as hot as they would with a two pipe system.

 

[koomber]

Didn't see it mentioned, but before you replaced the radiators did you happen to check how hot they were?

How hot does the feed pipe at the boiler feel? Is the water leaving the boiler hot?