System or Combi in local pub?

[JohnHuson]

23 rads and one kitchen hot water supply plus two basins in toilets. Had an old Concorde system boiler which gave up.
Two zones supplying two large rooms 50' x 12' x 24' each. Local heating company recommended Nevien 42kw combi
boiler and things went wrong after that.
The installers have made excuses that the building needs the radiators, which worked fine before, at a cost of £1400
or they would disown the installation with much chattering of balancing the system etc. I have done that and vented a
number of times. ( I am an old fart who has worked and maintained many systems, but not the gas.) My problem boilers
were Worcester Bosch. I learnt to replace PCB parts at 30p from Maplins instead of paying £120 for a new board.
The boiler keeps blowing seals and is not happy with the system pressure.
Landlord was advised to install another pump as the heating took four hours to circulate to the lover zone radiators but
not to the extremities. The boiler has to lift the supply to the roof space and is a 40mm pipe work.
Its a mess and the Publican has lost customers owing to the lack of heating.
He has appealed to Nevien who have been helpful and initially said that the 42kw boiler will cope with the system.
They have since changed their position after their engineer changed the seals and said a system boiler was the best fit.
The original tank is still in place.
Nevien seem to be putting pressure on the local installers to sort things out but they are pratting around and making as many excuses
possible to avoid the issue.
Could you please advise me regarding the room volumes if a combi boiler should provide the heating system?

 

[John.g]

Do you absolutely know that the "bursting" seals are on the central heating side ?, strange, because if so, the boiler PRV, in lifting at 3bar, should prevent just such a occurance, if the problem is coming from the DHW side then it would mean a extremely high mains pressure which hasn't a pressure reducing valve (PRV) installed.

 

[JohnHuson]

Its certainly unconventional but I'd venture that there are systems with pumps installed like this and working OK, as pointed out above, two different head pumps in "series" may cause one to fight the other, they are really not in series in accepted pump jargon where both pumps are installed one immediately behind the other, but generally one would then install one pump with the required head.
In your case, the boiler circ pump pumps from the return, through the boiler Hx and then supplies the 8M pump.
I would suggest trying to establish what the flow rate is from other data to hand, the boiler flow and return temps and the boiler output, is all you need but these three values arn't often available from the boiler display but the flow/return temps can be measured on the pipes which will give some info at any rate, the boiler output is more difficult but if both zones are open then maybe can get a good idea. If that 8m pump displays its power in watts? (W) then flow rate can be derived exactly, from the pump curves.

Thank you for all your input. It is appreciated. The system is still under performing. Now waiting for Navien engineers assessment of the situation. This should not be so when the customer has spent £3000 with professionals?

 

[EvilDrPorkChop]

This should not be so when the customer has spent £3000 with professionals?

Well that's probably part of the main issue, he needs to spend a lot more than that on materials and the right contractor to get a solution that'll work!