Central heating not circulating after New Navien Combi fitted to Santon Premier system.

[JohnHuson]

I enjoy a pint at my local pub/restaurant owned by a hardworking Chinese family. I have had many years experience on property maintenance and they asked for my help.
He had an old LPG gas boiler feeding a Santon Premier unvented cylinder feeding 23 radiators and hot water for the kitchen. New boiler is a Navien combi and the pipework is a work of art!
The installers came out again and said boiler works as it should so problems is not of their making.
The upstairs living accommodation has a separate combi system.
When the fitters arrived he was given an option to retain the unvented cylinder, so he did.

The central heating no longer circulates around the building and about six radiators get warm.
I have bled and done everything to get it going but no improvement. It worked fine before the boiler change. The system was not drained. It was flushed four years ago. All TG's are working fine.
I notice that the original central heating Granfoss pump sucks the flow downwards to the cold feed of the cylinder at the bottom as a secondary feed. I found that the water temperature between 2 feet from the pump to the cylinder went from warm to cool indicating lack of flow?
I cracked open the drain cock and the temp from the pump to the cold supply into the cylinder is now even.
The expansion vessel is at 3 bar pressure.

I changed the pump to a nearly new pump which is working as it should. Still no improvement.
The problem is either; the installation of the new combi boiler? The routing of pipework not being correct? Or me not seeing the obvious?
Your help appreciated please. They are really nice people and I might get a couple of freebie beers.

 

[ShaunCorbs]

Pictures?

 

[snowhead]

Confused,
The system worked before the new boiler was fitted I assume.
Someone has fitted a replacement and now the system doesn't work and it's not of their making.

A couple of things,
To be able to say it's not of their making they'd need to know exactly what the issue is, so should be offering to fix it even if it means charging more than originally quoted.
They're the best positioned to fix it, they know how the old boiler was piped and how they've piped in the new boiler.

But they clearly don't know what the issue is, otherwise they'd have said as defence of why it wasn't of their making.

It would be the same as driving a car to a garage for a new engine, the garage fitting it and it starts but the car won't drive and the garage saying take it away the problem is not of their making.

My guess is that they maybe good boiler fitters, or even excellent, but have no understanding of heating systems and faults.

 

[JohnHuson]

System worked fine with the old LPG boiler, now does not since they adapted the new combi boiler to
work with the Santon Cylinder. It was the customers decision to retain the cylinder and now the heating
will not circulate. The boiler is producing heated water OK.
I agree with you regarding the installers.

 

[JohnHuson]

System worked fine with the old LPG boiler, now does not since they adapted the new combi boiler to
work with the Santon Cylinder. It was the customers decision to retain the cylinder and now the heating
will not circulate. The boiler is producing heated water OK.
I agree with you regarding the installers.

My Chinese friend has a pub and restaurant for past five years. They work hard and the UK is their future home.
The old Ideal Concord LPG boiler was knackered. They needed a quick solution so found an installer who could provide
a solution within days.
The Ideal Concord system was working well before the boiler expired. It was servicing the kitchen domestic outlets and four toilet
hand basins plus 23 radiators at various levels. The system is mainly 15mm to the rads and a lot of 22mm in the loft
and supply flow.
They installed a Navien 40kw domestic boiler in a commercial kitchen. They were assured that it would do the job.
The customer was most aware that if the Combi boiler failed to operate; the Concord cylinder storage with immersion was a back up and
would be a good idea.
New boiler is now installed. The central heating is not working. The first few rads will heat. If we balance the system we can get warm rads.
We asked the installers to come and solve the problem and the boiler was leaking water from the casing. They did attend very quickly and replaced
a seal on the cold supply to the heat exchanger. They charged £200 under guarantee for 35 minutes work.

We now have a system which provides good domestic output but no radiator heating to most of the area where it worked well before the boiler
change.
The installer says the 23 TRV's need to be changed at an extra cost of £1300 to solve the problem.

 

[ShaunCorbs]

Do you know the old size of the concord eg kw and the new one ?

 

[JohnHuson]

Do you know the old size of the concord eg kw and the new one ?

Hi, It was a floor standing CX LPG about 25 years old. Will check output this evening and reply.
Thanks.

 

[ShaunCorbs]

So probably 60kw

 

[SJB060685]

If Shauns guess is correct and the original boiler output was around 60kw, then a new boiler with a maximum output of 40kw is not man enough.

 

[JohnHuson]

So probably 60kw

Hi, it was a 40 CX so I assume 40kw same as new one?

 

[ShaunCorbs]

Yes so that in theory is good

Did they remove the external pumps ?

 

[JohnHuson]

No changes were made to the radiator system apart from adapting the 40KW combi to the system and the non vented
cylinder remained as it was. My concern is that is a combi 40KW combi capable to feed a system with 22 to 54mm
feed around two zones? This is a Pub so the 23 rads need a supply which can be quick and efficient. We have now got
heat in around nine of the 23 rads. That has taken two days of the boiler running.
The system has been purged of air, rads bled, drain feeds on each point to at least 10 gallons drained.
I would add that the system worked well prior to the installation of the new combi boiler.
The installer has suggested the TRV's are stuck. They are not, and the flow of water within the circuits are free of problems.

 

[ShaunCorbs]

And the old pump was it removed or left in ?

 

[JohnHuson]

And the old pump was it removed or left in ?

The secondary pump was changed but was working fine on all three speeds so original pump was refitted.

 

[ShaunCorbs]

Any chance of a few pictures of how they have pipes it ?

 

[JohnHuson]

The secondary pump was changed but was working fine on all three speeds so original pump was refitted.

The original pump in the old boiler was scrapped when the boiler was removed. The Combi internal pump
I hope is doing its job. The secondary pump on the cylinder cold supply is working as it should.
This is driving me nuts!
Either there is a circulation problem caused by lack of pump pressure from the ne combi or a restriction that
has suddenly appeared on the change over?

 

[ShaunCorbs]

There you go the internal pump of the new boiler is not man enough for the system it needs the old pump back on / one sized correctly

 

[JohnHuson]

There you go the internal pump of the new boiler is not man enough for the system it needs the old pump back on / one sized correctly

I guess you are right. If it needs an additional push pump where in the system should it be located to move things around?

 

[ShaunCorbs]

Should be after the llh

I hope there’s additional expansion tank / tanks ?

 

[SJB060685]

Sounds like you need to separate the system. Also is the old boiler a non condenser @ShaunCorbs and the rads possibly ∆T 60?

 

[JohnHuson]

Should be after the llh

I hope there’s additional expansion tank / tanks ?

Thanks Shaun but I did not get the last word meaning? iid?

 

[ShaunCorbs]

Sounds like you need to separate the system. Also is the old boiler a non condenser @ShaunCorbs and the rads possibly ∆T 60?

Yep

Low loss header as condensing boilers don’t like older systems tbh I would fit a plate heat exchanger to save the new boiler as I doubt they cleaned the system

 

[JohnHuson]

Sounds like you need to separate the system. Also is the old boiler a non condenser @ShaunCorbs and the rads possibly ∆T 60?

No, the old boiler was a 20 year old Ideal Concord CX40 floor standing unvented.

 

[JohnHuson]

Are you in travelling distance of Chester?

 

[ShaunCorbs]

About 10 miles away but I booked up sorry