Can't get return temp down, are those rads / pipe (photos) the problem?

[Matt723]

Hi All

This is the set-up:

5 beds, victorian, ~1800 sqft, 12 radiators (including 3 towel rads, one in each bathroom / en-suite). Vaillant ecotec 637 plus S-plan.

There was weirdly an additional grundfos pump ups2 on top of the internal pump in the boiler. This pump is disconnected so only the internal remains (all rads get hot anyway).

Estimated rads output is ~17 kw, average of 3 online calculators. These are the dimensions:

Temp differential: all rads fully open, boiler ramping up, ~ 10 degrees difference. When all the rads are warm (okay to touch but not for long, seems right temp) the return temp starts to go up and the differential will stabilise at 8/5 degrees. If some rads are closed (e.g. guest room, office) then the differential will be no more than 5 degrees (ie 68 flow, 63 return).

No cycling, although 37 kw/h is massive the boiler can stay on modulating at minimum output with enough rads on, so that's not the issue. Also the rads do get hot as mentioned.

On DHW it's a similar result. The cylinder is 5m from boiler and fairly recent (Zircon 250l, 7y old), flow is at 75 degrees and it will come back at 70 after going through the coil.

Internal boiler pump is on auto for DHW which is almost always at 15%. For DHW it goes the pump value is at 70%.

The house take hours to heat but to be fair it's -2 outside at night the days.

Regarding pipe work, it is 22mm downstairs where the new boiler / cylinder cupboard was set-up 7 years ago. Where the rads are it looks like this:

(Unsure if this is single or double pipe circuit.)

In your opinion what is the reason why there is only a 5 degrees differential, and how can the situation be improved?

Thanks

 

[JohnD]

Please explain how (or if) you balanced the system.

OOI when I had a 5-bedroom detached Edwardian house, I had a 30kW boiler and rads big enough to dissipate it, and it was only just enough.

Is yours detached? How thick is the loft insulation? What is your calculated whole-house heat loss calculation?

 

[Matt723]

Not balanced by myself. All rads seem to get equally hot (to the human touch, not tested with a particular device). Should anything be done on this front?

 

[JohnD]

Balance them.

See my updated post above.

If the radiators are fully hot and the house is cold, then your radiators are too small to heat the house.

 

[JohnD]

Balancing

When balancing, close all the lockshields, and open by half a turn. No more.

Then run the CH for half an hour.

Use the temperature sensors in the skin of your hand. The flow pipe should be "too hot to hold" and the return pipe should be "too hot to hold for long."

For any that are not, open or close the lockshielc by no more than a quarter turn, and continue running the CH for another half hour before checking again. Do not alter any by more than a quarter turn in half an hour. The adjustment is very slight, and it is all at the "nearly closed" position.

Once flow seems correct, and has been for half an hour, feel them all over. Top, bottom, sides, middle. There should be no cold patches. They should be hotter at the top than the bottom. If any are excessively hot, you can tighten the lockshield by a quarter turn.

Some rooms may have rads that are too big, and you can reduce their output by tightening the lockshield. A radiator that is too small for the room cannot be made more powerful.

Write the adjustments in a notebook and tie it to the boiler.

 

[BlueLoo]

Balance them.

See my updated post above.

If the radiators are fully hot and the house is cold, then your radiators are too small to heat the house.

How does balancing (throttling heat output) help in this situation?

You want the rads on full pelt.

 

[JohnD]

It will ensure that all rads heat up equally quickly

And it can give you the temperature drop you seem to be concerned about

Though I doubt that is the real problem.

I think your radiators are too small for your house and the boiler is bravely but unsuccessfully trying to deliver more heat than they can dissipate.

 

[BlueLoo]

Hi All

This is the set-up:

5 beds, victorian, ~1800 sqft, 12 radiators (including 3 towel rads, one in each bathroom / en-suite). Vaillant ecotec 637 plus S-plan.

There was weirdly an additional grundfos pump ups2 on top of the internal pump in the boiler. This pump is disconnected so only the internal remains (all rads get hot anyway).

Estimated rads output is ~17 kw, average of 3 online calculators. These are the dimensions:

View attachment 323639

Temp differential: all rads fully open, boiler ramping up, ~ 10 degrees difference. When all the rads are warm (okay to touch but not for long, seems right temp) the return temp starts to go up and the differential will stabilise at 8/5 degrees. If some rads are closed (e.g. guest room, office) then the differential will be no more than 5 degrees (ie 68 flow, 63 return).

No cycling, although 37 kw/h is massive the boiler can stay on modulating at minimum output with enough rads on, so that's not the issue. Also the rads do get hot as mentioned.

On DHW it's a similar result. The cylinder is 5m from boiler and fairly recent (Zircon 250l, 7y old), flow is at 75 degrees and it will come back at 70 after going through the coil.

Internal boiler pump is on auto for DHW which is almost always at 15%. For DHW it goes the pump value is at 70%.

The house take hours to heat but to be fair it's -2 outside at night the days.

Regarding pipe work, it is 22mm downstairs where the new boiler / cylinder cupboard was set-up 7 years ago. Where the rads are it looks like this:

View attachment 323640
(Unsure if this is single or double pipe circuit.)

In your opinion what is the reason why there is only a 5 degrees differential, and how can the situation be improved?

Thanks

Turn the pump or the boiler down, but then you can't get enough heat into the rads...

Fix the easy stuff 1st. Insulate the piping in the voids. Remove the dead pump. Check the boiler settings and system controls.
Are they ****e? Upgrade themrud.
Is the system full of crud? Drain the system, Remove the rads, hose them out, clean out the tanks etc, flush, add cleaner, flush again. Inhibit.
Draw the system out. Show the drawings here. Is something stupid happening?

I don't agree with balancing in modern systems. The trades are addicted to it.
Get a pen and paper, mark out each rad and close the lockshields, taking note of how many turns they take. Then, open them up fully. See what happens. Does the system like full flow?

Whilst you have the system drained, think about adding trvs. Cheap and easy. And so on and so forth.

I'm going to say it's muck clogging the system up and a badly set up boiler and control.

Best of luck.

 

[JohnD]

I don't agree with balancing in modern systems.

Feel free to explain why you think there are undesirable consequences from heating all rooms equally quickly.

 

[JohnD]

I'm going to say it's muck clogging the system up and a badly set up boiler and control.

He says all the radiators are hot.

Explain what you think sludge is doing.

 

[BlueLoo]

Feel free to explain why you think there are undesirable consequences from heating all rooms equally quickly.

You mean equally slowly.
Speed is the problem here.

 

[JohnD]

No, I mean quickly.

When all the hot water rushes through the easiest rads, distant rooms will get less (or none) and heat up slowly, or not at all.

I don't think you understand what balancing is.

 

[BlueLoo]

He says all the radiators are hot.

Explain what you think sludge is doing.

Sludge, crud, magnetite etc.
Dead zones, low spots, blockages, blah blah.

I clean my radiators out periodically (take em off and flush them out) and the difference going back is astonishing. Not that they are poor in the 1st instance.

 

[JohnD]

Sludge, crud, magnetite etc.
Dead zones, low spots, blockages, blah blah.

I clean my radiators out periodically (take em off and flush them out) and the difference going back is astonishing. Not that they are poor in the 1st instance.

You haven't explained what you think sludge is doing to cause him a problem.

 

[BlueLoo]

No, I mean quickly.

When all the hot water rushes through the easiest rads, distant rooms will get less (or none) and heat up slowly, or not at all.

I don't think you understand what balancing is.

I do.

It's not a permanent suggestion hence the comment to note the position.