System or Combi in local pub?

[JohnHuson]

Excellent precise information, thank you and to all others who have contributed. Cheers, John.

 

[JohnHuson]

Thank you for all the responses. They are waiting for a Navien engineer to attend to replace
the heat exchanger under guarantee? Why does that need replacing?
In the meantime the boiler pressure can only be supplied if the cold water pressure supply is
being balanced by the pressure valve constantly sending cold water supply to the outflow
resulting in hundreds of gallons being wasted every day. I thought it was a local offence
to waste water? it is the only way he can get heating in the pub.
What a mess.

 

[John.g]

Are you saying that the Boiler PRV (safety valve) is lifting at 3 bar and discharging water which then has to be replaced with cold water?

 

[SJB060685]

Are you now saying the plate heat exchanger for HW has failed and the PRV is lifting?
If so then yes you will be losing water but hundreds of gallons a day I highly doubt.
This seems to be getting worse and worse. You need a reputable engineer to go over the whole system. I’m not going to read or comment on this thread further. We’ve given you the advice you need, you now need to get someone out who actually knows a thing or two.

 

[JohnHuson]

Are you saying that the Boiler PRV (safety valve) is lifting at 3 bar and discharging water which then has to be replaced with cold water?

Yes, stupid isn't it! They are going to replace the heat exchanger so it seems. Several seals have burst causing water leaks since installation. What mess. I find it difficult to accept the inept performance and lack of knowledge from the installers.

 

[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!