Cool radiator - flow issue? Help please!

[Nlondonlem]

Hello, I am looking for some advice please to resolve problems with our central heating system.

To give some info about our system: We have a 2 year old regular 100W WB1B Viessmann 19kW Regular Boiler in a downstairs cupboard with an Ariston 210L unvented cylinder and Grunfos Alpha 2L 15-60 130 pump in an upstairs cupboard on 2[SUP]nd[/SUP] floor. We have a 4 bed ten year old mid-terraced 3 level town-house, with 2 en-suite shower rooms, 1 master bathroom, guest toilet and 14 radiators (of different sizes). The boiler, pump and motorised valves are 2 years old (old ones died week we moved into the property!) and the unvented cylinder is 3 years old. System has been looked after with inhibitor since we owned it and the boiler serviced every year. We do not believe the system was well maintained (as old boiler was a rust bucket!) before we moved in.

I have enclosed a photo of our upstairs system adjacent to the unvented cylinder

Problems are:

1) One downstairs radiator in our former garage (newly converted into a room) does not get very hot and my builder & plumber have no further ideas to get it providing more heat output.

2) My Alpha 2 pump only performs adequately if it is set to constant pressure 3 (far left on display mode 3) which is quite noisy. In the instructions it seems to suggest that Highest proportional-pressure curve (PP2) is the appropriate mode but the radiators don’t get hot enough using this mode.

Based on reading great advice on forums so far I have tried:

• Closing off all other rads and forcing water through the cold radiator. It warmed up relatively well on its own.
• Checked TRVs are not sticking. The TRV on the cold radiator is a new Drayton TRV4
• I opened up other radiators and since the building works I have been bleeding a lot of gas (not sure if air/hydrogen/both) from radiators mainly upstairs. I have also had some radiators sporadically going cold and have managed to force out air locks now. The only radiator now causing a problem is the garage one.
• I have also bled air from the valve adjacent to cylinder, magnaclean and the manifolds. The pump self-bleeds on high CP setting.
• I have followed guides to balance the radiators and set TRVs appropriately. This has helped balance heat around the rest of the house a lot, other than this one room

Questions:

• Could it be worth taking the radiator off and flushing it with a hose?
• If you look at the photo provided:
  • Does it look like the area marked is a manual bypass valve?
  • If so, could it be that the bypass valve is too open and reducing my flow around the CH system to downstairs?
  • Would it be worth fitting an automatic bypass valve?
  • Is the Grundfos pump the right way around (arrow is down) and/or is it drawing air into the system?
• Would a secondary circulating pump help with flow and where would you place it (downstairs?)
• Do you think my boiler size of 19 kW is appropriate for this size of property?

Apologies for the long message, I wanted to make sure that I provided sufficient info to help with the diagnoses and what I’ve already tried!

Thank you in advance for your time and help
L

 

[rpm]

Welcome to the forums, can`t help you myself however great first post there.

 

[Nlondonlem]

Thanks rpm! I've made sure to use existing forum posts to learn and self-diagnose as much as possible first, but now recognise I need more help so wanted to provide as much context as I could. :smile5:

 

[rpm]

The only things I picked up on were, the radiator in the garage is the new one and therefore might be the last one in line so a lot depends on how it has been added to the system and the pump normally is set to the 2nd speed not the 3rd however sure others will be along later to advise better.

 

[johnf]

Certainly looks like a manual bypass valve. Try closing it and running the heating and see what happens. It also depends on how radiators have been piped. For instance you cant just keep adding radiators to 15mm heating flow and return pipework. How many radiators are fed from 15mm pipework including the one you added and what output are they? It may be that you are just trying to feed too many rads and you need to take the flow and return back to a point where you can "T" into 22mm pipework.
When the system was drained to add the new rad, what condition was the heating system water?

 

[Chalked]

Hi
Did you see where the new radiator was connected into?
Could you post a picture of the offending radiators.

 

[ShaunCorbs]

Have you balanced the rads ??

And output sounds ok

 

[Chalked]

Wonder if it's teed into 10mm!

 

[Nlondonlem]

Hi all,
Thank you for your suggestions and follow-up questions. Answers below:

1) I tried closing the manual bypass valve and running heating only. The radiator heated up a little bit more but not significantly so. The TRV is on the flow and the inlet pipe is hot but the lockshield on the return is cold. Why could this be? Could it be worth taking it off and flushing it out with hose? The radiator doesn’t look that old. I have seen guides online and I’m confident to have a go.

2) The water appears clean from drain down and when removing air from rads

3) I have balanced the rads following online guides, which has made an improvement to get balanced heat over the floors and other radiators, aside from this stubborn radiator

4) Our house has plastic micro-bore with <15mm pipe via manifolds on the floors. It looks like this rad was taken as a tee off one of the ground floor rads in the hallway and they have used 15mm copper pipe from that rad. The feeder rad gets pretty warm but not as hot as others. I have tried minor adjustments to the lockshield valves for the feeder and garage rad to balance flow between them but don’t think it improved anything. Unfortunately getting back to the manifold will be a challenge as the hallway is tiled. I suspect this is why the previous owner went for cheaper option of taking a spur off the hallway rad. Would a second circulating pump help if placed downstairs?

Photo of rad attached

Thanks all!
L

 

[Chalked]

Hi again.
The rad needs connecting unto the main pipework 22 or 15 mm. It will never work connected into a rad fed by 10mm. For flow reasons, when Tnis is done, both rads don't work. Your installer should rectify this, as they should have known better.

 

[Riley]

As stated pipework will not be able to supply enough energy/heat if teed into. Needs its own feed

 

[Nlondonlem]

Hi all - good news... problem solved!!

In frustration & desperation I went around the house checking all the trv valve pins moved freely, re-tried adjusting the manual bypass valve, gave the offending radiator and one feeding it plus pipework some firm taps to see if I could clear any debris, and adjusted the lockshield valve of the bad radiator plus one feeding it to balance flow between them... left system running for a while and came home to a hot house. It's the hottest it has ever been in the house and particularly downstairs. The bad rad and one feeding it are both hot too. Very pleased!! :54:

Would you recommend changing the manual bypass valve to an automatic one? I'm surprised it wasn't changed when the boiler and pump were replaced 2 years ago! (now that I know what one is!)

Thanks all

 

[ShaunCorbs]

Yes would be better