Intermediate Heat Exchanger

[TCH]

Folks, need some advice.

I have a large, long "bungalow" with a Vaillant ecotech plus 630 at one end driving a closed/megaflow type system. It's a long way to the other end.

We have mixed heating types: Traditional radiators, underfloor for the extension and polypipe overlay for the sitting room.

The Vaillant struggles often giving an F.20 error (especially when just heating the water cylinder in summer).

A plumber suggested we consider installing an intermediate heat exchanger with separate pump next to the boiler separating the boiler from driving the system and allowing it just to heat water.

Unfortunately, I lost the plumbers number and cannot remember what the type of system is called or find any reference to it on the internet.

Q:
What is this type of system called?
Is it a good solution?

No, I can't move the boiler to somewhere in the middle of the house

Cheers,

Tim

 

[Harry Bloomfield]

The Vaillant struggles often giving an F.20 error (especially when just heating the water cylinder in summer).

F20 means the boiler has shut down on too high a temperature. I'm no expert, but to me that suggests no or not enough flow of water through the boiler/ your system has too much back pressure/ your pump is not moving the flow fast enough.

Maybe install a more capable pump, or check there are no restrictions to the flow?

 

[TCH]

F20 means the boiler has shut down on too high a temperature. I'm no expert, but to me that suggests no or not enough flow of water through the boiler/ your system has too much back pressure/ your pump is not moving the flow fast enough.

Maybe install a more capable pump, or check there are no restrictions to the flow?

Many thanks HB for you quick response. The system is fairly new and has always given us this problem. Yes, def not getting the water around and another pump may help but his main thought was is it a long way from one end of the house to the other.

 

[oldbutnotdead]

How new is 'fairly new'? It sounds like a commissioning failure, sticking a thermal store next to the boiler would stop that error code appearing bu will cost you a chunk of cash and a chunk of space.
Was a bypass valve installed? What size pipes are running from the boiler rhrough the house? What temperature is the boiler set at (not the room thermostat, the actual boiler). Are there any motorised valves on the system? Any balancing valves been forgotten about?

 

[dilalio]

Low loss header.

 

[Gasguru]

The fault is almost certainly down to poor installation...F20 is a proper overheat ie. the flowrate is dropping so low that the boiler doesn't even have a chance to fault with the usual fault codes when it struggles to dissipate the heat.

I'd guess the plumber is talking about decoupling the boiler from the different heating circuits using a Low Loss Header or a Buffer vessel. This allows the boiler to so its own thing whist the heating/hot water circuits do theres and they each remain happy. Both systems are beyond your average heating installer and it's normally only necessary for very large domestic properties and commercial systems.

These large system boilers often have insuffiently sized expansion vessels and pumps ad this gives rise to the problems.

A 30kW boiler seems very excessive for a bungalow...a starting point would be to check there is always sufficient flow through the boiler regardless of demand and to de-rate the boiler output.

 

[TCH]

How new is 'fairly new'? It sounds like a commissioning failure, sticking a thermal store next to the boiler would stop that error code appearing bu will cost you a chunk of cash and a chunk of space.
Was a bypass valve installed? What size pipes are running from the boiler rhrough the house? What temperature is the boiler set at (not the room thermostat, the actual boiler). Are there any motorised valves on the system? Any balancing valves been forgotten about?

Approx 5 years old now. Everything was replaced including pipework. Motorised valves everywhere. Rads have Thermostatic valves as well. No bypass valve installed; it was discussed with the recent plumber but due to the size of the property and combination of heating requirements he felt a "low loss header" would be a better solution. Boiler temp is 70 for the central heating and 65 for the hot water.

 

[TCH]

The fault is almost certainly down to poor installation...F20 is a proper overheat ie. the flowrate is dropping so low that the boiler doesn't even have a chance to fault with the usual fault codes when it struggles to dissipate the heat.

I'd guess the plumber is talking about decoupling the boiler from the different heating circuits using a Low Loss Header or a Buffer vessel. This allows the boiler to so its own thing whist the heating/hot water circuits do theres and they each remain happy. Both systems are beyond your average heating installer and it's normally only necessary for very large domestic properties and commercial systems.

These large system boilers often have insuffiently sized expansion vessels and pumps ad this gives rise to the problems.

A 30kW boiler seems very excessive for a bungalow...a starting point would be to check there is always sufficient flow through the boiler regardless of demand and to de-rate the boiler output.

All, really grateful for the fast feedback.

We discussed a bypass valve but he thought "decoupling the boiler from the heating" would give a better and more consistent result.

Although it's a bungalow, it is a pretty large 5 bed property, 2 bath and 3 reception. Sitting room/kitchen is approx 80M Sq polypipe overlay, 2 main beds are traditional underfloor, the rest is radiators. The furthest point is approx 40M from the boiler and it struggles to deliver heat evenly across the three different heating solutions.

The original plumber moved away before the job was really complete. Just managed to get him to finish it.

I'll get some quotes in. Winter is coming

Tim

 

[Harry Bloomfield]

Approx 5 years old now. Everything was replaced including pipework. Motorised valves everywhere. Rads have Thermostatic valves as well. No bypass valve installed; it was discussed with the recent plumber but due to the size of the property and combination of heating requirements he felt a "low loss header" would be a better solution. Boiler temp is 70 for the central heating and 65 for the hot water.

You mention a long pipe run, how long (roughly) to and from the boiler, to where it first branches off the flow and return pipes? What size pipe has been used?

It is obviously an inadequate flow through the boiler problem, which means the pipes are too long/ too small/ pipes obstructed/ the pump not pumping enough.

 

[Harry Bloomfield]

The furthest point is approx 40M from the boiler and it struggles to deliver heat evenly across the three different heating solutions.

The furthest point is not important, what matters to the boiler F20 issue, is the nearest circulation loop in the circuit. Your problem with the furthest point will only affect getting heat to that area.

 

[Gasguru]

The boiler already has a bypass (although it may not be set correctly).
Has anyone tried setting the D014 parameter to 5 to force the pump to run at maximum speed?
I'd also pull up the status code menu to see what codes you're getting before is faults...might see a few S53s.

 

[oldbutnotdead]

Pipe sizes from the boiler? Is everything manifolded off (probably not if you have motorised valves everywhere). I'm wondering (since this has been happening from Day 1) whether the controls have been wired correctly with any run-on time for the motorised valves.

 

[TCH]

Ok, I've had a look at the boiler faults and it looks like I'm getting a lot of F.23s and a few F.20s.
I can't get into the menu to check settings - I have the user and install PDFs but it's not playing ball. Also noticed both the flow and return pipes are leaking under the boiler.

Maybe time to junk the boiler and get a new one

 

[oldbutnotdead]

I'd want a bit more than 5 years from a boiler...no idea on the fault codes (@Gasguru looks like the oracle there) but sounds rather like a bodged install. 40 metres is a long leg but its all on 1 level so with appropriate pipe sizing can work fine. What size are the flow & return?
You say you can't relocate the boiler to the middle of the bungalow but would there be space for a low loss header or buffer tank somewhere more central?

 

[Gasguru]

F23 and F20 are both related to temperature and are consistent with poor flowrates.
Get a new boiler by all means but if not installed properly you're back to square one.
Unfortunately very few in the trade understand that modern boiler heat exchangers have huge resistance and you can't just pipe them up and expect them to work with any system.
Vaillants more than other makes appear sensitive to heat output versus flowrate.