New boiler but extension still not hot

[WillieB]

Hello, We had an extension built seven years ago. Initially the builders' plumber connected the heating to the house system but this didn't work. The builder got him out again and he created a separate heating circuit from the boiler (ie one circuit for the house, the other for the extension).

This worked well till we had to get a new boiler (Viessmann) three months ago. Our own plumber (nice chap, used him for years!) power-flushed the system and flushed each rad by hand. Since then we have had trouble with getting the three rads in the extension to work together.

The wet room rad (R1) is always hot. R2 is hot since it was last balanced. R3 was cold then hot but is now stone cold again. Our plumber thought we might have a blockage but a high-strength cleaner and bleeding and balancing appeared to have worked -- we have had all radiators hot for a heady 48 hours.

So to my questions:
:: In the initial system the builders' plumber put TRVs on R2 and R3. With the separate system he gave us a Honeywell thermostat just for the extension. Could these be fighting each other?
:: The pipe out of the wall to the lockshield side of R3 gets hot while R3 itself stays cold. Could the builders' plumber have put the TRVs on the wrong side of the rads?
:: With the out and return pipes (see illustration) one is hot and the other usually but not always only lukewarm. Is this usual (regular builder is on holiday somewhere exotic at the moment, so I can't ask him)?

What I haven't mentioned so far is that the room is home to a grumpy octogenarian who seems to take personally our failure to get her heating going. With that in mind, any and all advice will be appreciated.

 

[ShaunCorbs]

If you turn just this zone eg with the three rads does the boiler fire up ?

 

[WillieB]

If you turn just this zone eg with the three rads does the boiler fire up ?

Yes it does.

 

[John.g]

Can you post a photo of this separate flow/return, is it just teed off the existing flow/return from the same side of the boiler as the "working" flow/return?

 

[WillieB]

Can you post a photo of this separate flow/return, is it just teed off the existing flow/return from the same side of the boiler as the "working" flow/return?

Thank you John G.

Pic 1 shows the underside of the boiler
Pic 2 shows the underside of the boiler from the left
Pic 3 shows the pipework to the right below the boiler (the cable is for an immersion heater on the tank)
Pic 4 shows the three heating controllers (the one at the top of the picture is for the extension)
Pic 5 shows what I think is the return with a magnet how's-your-father to collect crud
Pic 6 shows the flexible pipes going to and from the extension. The tall one is the out, the small one is the return.

I hope that helps!

 

[John.g]

Do those flexible pipes run all the way to the extension, what is the ~ distance from the boiler to the extension and what diameter are they?.
Any idea of the isolation ball valves make?, some ball valves have reduced bore unless full bore specified.
What model/power Viessmann?, if the extension is running on its own does the boiler cycle on/off?.

 

[John.g]

What is the total extension rads output?

 

[ShaunCorbs]

Yes it does.

Do these rads heat at all / does the boiler stay on etc

 

[WillieB]

Do these rads heat at all / does the boiler stay on etc

Hello, yes they do -- and the boiler stays on. As mentioned previously, at first it was just R1. I then had a go at balancing the system and got R2 and R3 working. R3 then dropped off the system, which is when I thought there may be a conflict between the TRVs and the room thermostat.

 

[John.g]

If you can give some more info re queries on post #6 & 7, might be able to figure something out

 

[WillieB]

What is the total extension rads output?

The flexible pipes run beneath the upstairs floor to 20mm copper pipes that come down the lounge wall. They then enter the "original" extension pipework, which is all copper (ie the pipework put in seven years ago and before the builders' plumber had to change his plans).
The boiler is on the upstairs, south side of the house, so the pipes fall 2.6m to the ground floor then 5.8m northwards before going a maximum of 7.5m eastwards, so 15.9m approx.
I don't know the power output of the rads in the extension but pix of all three below. Widths of the ordinary rads are 81cm (R3) and 51cm (R2). The bathroom rad (R1) is roughly the height of a door.
I should say that apart from the original glitch (and two pipes that rubbed together under the concrete floor and led both to burst -- but that's another story) the system worked OK till we got the new boiler.

 

[John.g]

Are you getting any air in the system?

What model Viessmann and output?

 

[WillieB]

Are you getting any air in the system?

What model Viessmann and output?

Hi, it is the Vitodens 100W, which I believe is their largest. We have 11 rads overall, including the three in the extension, so they account for about 16.5kW Max, which is half the boiler's output. No, we are not getting any air in the system.

 

[Craig Watson]

Well apart from the horrendous pipework (which really does make you question the competency of the installer) the 2 main things jumping out at me is the 15mm feeds to the extention, ideally should be 22mm to atleast the first rad, but you say they used to work. So the next problem could be where the return connects back into the system. Where its tee'd in, it's above the main return to the boiler and has no air release there, could be a partial airlock restricting flow, or if the bypass valve is open/partially open, that could also be interrupting circulation on the extention side.

 

[WillieB]

Well apart from the horrendous pipework (which really does make you question the competency of the installer) the 2 main things jumping out at me is the 15mm feeds to the extention, ideally should be 22mm to atleast the first rad, but you say they used to work. So the next problem could be where the return connects back into the system. Where its tee'd in, it's above the main return to the boiler and has no air release there, could be a partial airlock restricting flow, or if the bypass valve is open/partially open, that could also be interrupting circulation on the extention side.

Thanks Craig. That will give me something to chew over. Happy New Year to you!

 

[ShaunCorbs]

I think it’s a system balancing issue as it works when it’s on its own and all get hot etc so I think the system is taking the parts of least resistance eg down the main heating circuits have you tried balancing the main side / did he open the lockshields when power flushing eg loosing the system balancing

 

[WillieB]

I think it’s a system balancing issue as it works when it’s on its own and all get hot etc so I think the system is taking the parts of least resistance eg down the main heating circuits have you tried balancing the main side / did he open the lockshields when power flushing eg loosing the system balancingHe reckons you can balance it via the TRVs rather than the lock shields. I d

 

[WillieB]

I don't know whether or not he opened the lock shields while flushing. He reckons you can balance via the TRVs rather than the lock shields, however I had some success a week or so ago using the lock shields. I'll try what you suggest. Many thanks.

 

[ShaunCorbs]

I don't know whether or not he opened the lock shields while flushing. He reckons you can balance via the TRVs rather than the lock shields, however I had some success a week or so ago using the lock shields. I'll try what you suggest. Many thanks.

You can’t balance via trvs

Edited

 

[John.g]

I think you implied that the boiler stays firing with the extension only on, if so, something doesn't add up because the minimum output of both the 30 & 35kw boilers is 8.0kw, (its 6.5kw for the 19 & 26kw.)

 

[WillieB]

You can’t balance via lockshields

I was following a guide on heating force dot co dot uk.

 

[WillieB]

I think you implied that the boiler stays firing with the extension only on, if so, something doesn't add up because the minimum output of both the 30 & 35kw boilers is 8.0kw, (its 6.5kw for the 19 & 26kw.)

Thanks. Will take a look at that again.

 

[ShaunCorbs]

I was following a guide on heating force dot co dot uk.

Sorry Was meant to say you can’t balance via trvs

 

[WillieB]

Sorry Was meant to say you can’t balance via trvs

Thanks . A happy new year to you!