New combi boiler and now downstairs rad not very hot

[Alss01]

Hi everyone

Hoping for some advice please.

New combination greenstar 35kw installed replacing 20 yr old fully working back boiler (15kw) Boiler in attic as recommended by plumbing company. One pipe system. 2 rads in lounge don't get hot just warm or sometimes one gets hot at top but stays cool at bottom. 3 rads in lounge in total but the 2 affected are last in line, one is new as I wanted some extra heat in cold spot by large bay window. Not helped by suspended wood floor.

Plumbers have been out 3 times, since installing in July, down rated boiler by 40%, rebalanced rads, changed pipework to 2 affected but still same problem. I have 3 rads, only one getting to temp and other 2 not as hot together as original 1 when back boiler was working. A chemical flush was used prior to boiler installation by plumbers.

Owner of company says it because it's a one pipe system and as good as it gets but I have a new boiler and heating which does not work as well as before. I have not paid for work yet.

Appreciate any guidance, thanks

 

[picasso]

It could be the pump speed is too high, are the flow and return pipes hot ?

 

[Jackrae]

Is boiler consuming correct amount of fuel ?
Has he connected the flow and return pipes correctly viz not swapped them over ?
If it was good before and not now so then clearly it's not "as good as it gets"
Your "new rad" might be contributing to the problem

 

[JonG1]

Have they fitted new TRV's by any chance and do you have a pipe running beneath each rad with the valves connected into it at each end of the rad, or does the pipework go into 1 rad valve and out of the other?

Like picasso says it could be pump speed, depending on the layout heat needs to fill each rad by gravity circulation, if the pump speed is too high the heat won't have chance to transfer to the rad. If they have fitted normal TRV's the resistance will be too great for the gravity transfer to occur.

 

[Alss01]

Hi, thanks for your replies.

Last visit the plumber did turn pump back down as he said the same as you all. I believe there is one pipe in one side and one pipe flow out the other side of rad. Pipe in is hot pipe out is luke warm on both problem rads.

When I had back boiler, the 2 original rads in lounge got hot first before rest of house so I do wonder if they are missing something with pipework in terms of flow direction. One last in run had its trv changed Friday to bidirectional trv ,rest of rads have trv except halfway rad, these were already fitted and worked with old boiler but otherwise not sure if they are 'normal' or not but guess they are. They did mention that rad may be full of sludge at bottom but that wouldn't explain why the new rad only gets hot at top as well, it's only 200mm high so I am losing half the heat capability. Also, after their 2nd visit when I had air in bedroom rad and was not warming up, rad last in run worked perfectly but new one didn't work at all. Bled bedroom rad and 2 downstairs not warming up.

The plumber mentioned a slight kink in pipe by last rad but wasn't sure if that had always been there or his company had done it and said he would look at this if I still had problems over weekend.

I guess if at next visit they don't fix it I have to get second opinion.

 

[Happyplumber]

Why was the system left on a one pipe system
When an old back boiler came out then the whole house shoukd have been repiped
The set up you have at best will work adequately but never as well as it has the potential to
If that was my home I would renew all pipework to actually benefit from a brand new condensing boiler

 

[Alss01]

I don't know. The plumbers came in, provided recommendation for boiler and quoted. The one pipe/2 pipe issue was never raised until after when it wasn't working. If they had recommended it I would have got it done, it's an old house and system and would prefer to get it done properly. I was a little annoyed when told by the plumbers a combination boiler would be much more efficient during quote and then after installing being told as it was a one pipe system it now wouldn't be. They had opportunity to check pipe system when they did survey.

Just noticed another old rad upstairs now leaking slowly from middle of rad which I am guessing as a sealed system is now finding weak spots.

Is it usual when bleeding rads downstairs to dribble out slowly and upstairs to 'bubble' out at high speed.?

 

[ScottishGasMan]

Sound like there is a restriction or incorrect piping to the downstairs rads.

As said, system should never have been attempted to fit onto One pipe, its just not how new boilers are meant to be fitted and directly opposes the manufactures instructions for new boilers in most cases.

Also any flushing done on a one pipe is essentially usless, should have been converted to two pipe then fully flushed.

Just get em back out and make a nusance to them till its done. if you get a second opinion the installing company are not obligated to pay for the next engineers time so you have to give them "Suitable" opportunity to put right first.

 

[Alss01]

Thanks, I will persevere and try to get them to fix it properly