What size boiler needed

[sherylryan]

I know, they just keep blaming our pipe sizes, but they are all ok. When he pulled the damaged baffles out I asked how did they get like that, his reply was the return water is to low at 46 c

So I guess we need to replace condensate pipe work

 

[sherylryan]

Boiler is set up for light oil,

 

[sherylryan]

Went and checked the condensate trap and found this:
Condensate trap was full and water had been leaking out on to the ground also found a lot of water lying inside on the bottom of the boiler.

 

[John.g]

No surprises there!!, just run the drain properly. Have you any spec on that light oil, not 100% sure if suitable for a condensing boiler but if so may require the burner to have a preheater somewhere, it might be in the specs.

 

[sherylryan]

No surprises there!!, just run the drain properly. Have you any spec on that light oil, not 100% sure if suitable for a condensing boiler but if so may require the burner to have a preheater somewhere, it might be in the specs.

No surprises there!!, just run the drain properly. Have you any spec on that light oil, not 100% sure if suitable for a condensing boiler but if so may require the burner to have a preheater somewhere, it might be in the specs.

It’s run on diesel, don’t think it has a pre heater. Sometimes when it’s behaving it’s self when the boiler starts up the pump will run first before the boiler fires up but not all the time.

 

[John.g]

Didn't think diesel allowed with condensate.nsing Firebirds.
The fan and direct coupled pump should run for ~ 7 sec purge time. The oil solenoid should then energise with ignition spark.

 

[exedon2]

Certainly all the Firebird boilers sold here are 28 sec fuel only .
Plus your plumber is a idiot to think that condensate waste is ok.
Manufacturer asks for minimum of one in two hundred fall.

 

[sherylryan]

Didn't think diesel allowed with condensate.nsing Firebirds.
The fan and direct coupled pump should run for ~ 7 sec purge time. The oil solenoid should then energise with ignition spark.

I wonder because they have taking the pump off from the inside of the boiler and fitted an external one that’s why it didn’t purge anymore.

 

[sherylryan]

Certainly all the Firebird boilers sold here are 28 sec fuel only .
Plus your plumber is a idiot to think that condensate waste is ok.
Manufacturer asks for minimum of one in two hundred fall.

Everytime I question him about the condensate waste he says it’s not a problem and the reason the pipe melts is because of our flow and return pipes, he thinks I’m an idiot .

 

[John.g]

I wonder because they have taking the pump off from the inside of the boiler and fitted an external one that’s why it didn’t purge anymore.

I'm talking about the oil pump not the water pump that's connected to the fan, the boiler fan runs for around 7 seconds to purge the combustion chamber of any explosive gases before allowing ignition. The original boiler circ pump may have been programmed to overrun for awhile when all zone valves close.

I think you should think about getting someone familiar with oil boilers if changing boiler output or whatever, the original burner didn't need changing as its rated down to 26kw with the appropriate nozzle.

 

[sherylryan]

I'm talking about the oil pump not the water pump that's connected to the fan, the boiler fan runs for around 7 seconds to purge the combustion chamber of any explosive gases before allowing ignition. The original boiler circ pump may have been programmed to overrun for awhile when all zone valves close.

I think you should think about getting someone familiar with oil boilers if changing boiler output or whatever, the original burner didn't need changing as its rated down to 26kw with the appropriate nozzle.

Ok Re the fan. A quick rundown on what the plumber (who is supposedly a firebird agent installer) has done.

New 35 kw boiler installed August 2019 (sized by installer after doing all calculations)

October 2019 first melted condensate trap hose (Steel trap)

May 2020 another melted condensate trap hose

June 2020 another melted pipe

June 2020 new pump installled ( as installer advised us flow and return pipes to small hence condensate trap hose melting)

July 2020 another melted pipe

August 2020 air vent added to flow pipe (installer now advised us air is in the system and this is causing melted pipes.

September 2020 another melted pipe, pump pressure turned down by installer as apparently pressure to high.

October 2020 another melted pipe, pump pressure turn up by installer as apparently to low

March 2021 another melted pipe, pump pressure turned up again as apparently to low.

April 2021 another melted pipe, pump pressure turned up again as to low.

October 2021 installer decided to downsize boiler from to 23 kw as now the boiler is oversized hence melted pipes and pump pressure turned up.

November 2021 boiler downsized to wrong kw output so now sized to 26 kw from 35kw.

April 2022 boiler still not operating correctly.

 

[John.g]

OK, what's done is done.
There may have been little if any corrosion damage done to the boiler while operating in the fashion it was, a good clean out and service by some one who knows what they are doing is maybe all that is required.
You say the same boiler installer did the house heat loss calculations which look professionally done, on paper, at least. Can you ask him what the heat losses are, ie watts/dT difference between required room temp & ambient or whatever.

What have you done with the condensate waste just now?,, does it have to be discharged to that higher level?, if so you need a pump set which firebird can advise on, you may be able to run it temporarily into a container, it will only be a liter or so daily.,
Are you running the boiler just now?.

 

[sherylryan]

OK, what's done is done.
There may have been little if any corrosion damage done to the boiler while operating in the fashion it was, a good clean out and service by some one who knows what they are doing is maybe all that is required.
You say the same boiler installer did the house heat loss calculations which look professionally done, on paper, at least. Can you ask him what the heat losses are, ie watts/dT difference between required room temp & ambient or whatever.

What have you done with the condensate waste just now?,, does it have to be discharged to that higher level?, if so you need a pump set which firebird can advise on, you may be able to run it temporarily into a container, it will only be a liter or so daily.,
Are you running the boiler just now?.

So apparently heat loss calcs are Area/R value = watts/C.

I have the condensate waste going into a container at a lower level. Yes the boiler is still running.

 

[John.g]

The above whole house loss is 929.2 watts, you gave a average dT of 11C, 11C/22C, which means a required boiler output of 10.22kw, I know the rads output is 15kw but with zoning/roomstats one would think that a boiler output of 23/26kw should be sufficient even if the ambient was 5C, dT 17C, required boiler output 15.8kw.

For interest, how many litre(s) of condensate are you collecting daily?.

 

[sherylryan]

The above whole house loss is 929.2 watts, you gave a average dT of 11C, 11C/22C, which means a required boiler output of 10.22kw, I know the rads output is 15kw but with zoning/roomstats one would think that a boiler output of 23/26kw should be sufficient even if the ambient was 5C, dT 17C, required boiler output 15.8kw.

For interest, how many litre(s) of condensate are you collecting daily?.

Re zoning/roomstats the floorplans I sent through the other day the trouble manifold controls the w/c, entry, dining, kitchen. stairs, Office, living all in one thermostat.

To be honest I have no idea how many litres of condensate we are collecting per day. I am picking from what i saw yesterday with the condensate trap full (that has has not been checked since last October) not a lot of condensate.

 

[sherylryan]

The above whole house loss is 929.2 watts, you gave a average dT of 11C, 11C/22C, which means a required boiler output of 10.22kw, I know the rads output is 15kw but with zoning/roomstats one would think that a boiler output of 23/26kw should be sufficient even if the ambient was 5C, dT 17C, required boiler output 15.8kw.

For interest, how many litre(s) of condensate are you collecting daily?.

Hi John , I’ve have checked the condensate trap again today and it is full with excess water lying in the bottom of the boiler under the baffles. The condensate trap has 220 mls in it, last checked it 48 hours ago. Also noticed some has flown out pipe but I’m wondering now if some of this is from the PRV as it flows into the same outlet pipe. Water full of soot.

 

[John.g]

The condensate trap should always be full of water even with little/no condensing, if the boiler is fully condensing (and it won't be) then based on your fuel consumption of ~ 23 LPD would result in ~ 22 LPD of condensate in your container but you should possibly be collecting ~ 6 to 10 LPD or ~ 0.5 to 1 liters/hr if firing continuously for 1 hour and pro rata. The PRV waste pipe should not be teed in with the condensate waste pipe and the PRV should not in any case be lifting, try and collect the condensate before any T.

In view of the the continued and sooted water would advise getting someone in ASAP who knows what they are doing to clean out and inspect boiler for any damage, take FGA etc, the condensate baffle is possibly perforated so all/most of the condensate will flow into the bottom of the boiler.

What is the flexible hose in the boiler flue for?. (post #33)

 

[ShaunCorbs]

The condensate trap should always be full of water even with little/no condensing, if the boiler is fully condensing (and it won't be) then based on your fuel consumption of ~ 23 LPD would result in ~ 22 LPD of condensate in your container but you should possibly be collecting ~ 6 to 10 LPD or ~ 0.5 to 1 liters/hr if firing continuously for 1 hour and pro rata. The PRV waste pipe should not be teed in with the condensate waste pipe and the PRV should not in any case be lifting, try and collect the condensate before any T.

In view of the the continued and sooted water would advise getting someone in ASAP who knows what they are doing to clean out and inspect boiler for any damage, take FGA etc, the condensate baffle is possibly perforated so all/most of the condensate will flow into the bottom of the boiler.

What is the flexible hose in the boiler flue for?. (post #33)

Air intake from the double wall flue

 

[sherylryan]

The condensate trap should always be full of water even with little/no condensing, if the boiler is fully condensing (and it won't be) then based on your fuel consumption of ~ 23 LPD would result in ~ 22 LPD of condensate in your container but you should possibly be collecting ~ 6 to 10 LPD or ~ 0.5 to 1 liters/hr if firing continuously for 1 hour and pro rata. The PRV waste pipe should not be teed in with the condensate waste pipe and the PRV should not in any case be lifting, try and collect the condensate before any T.

In view of the the continued and sooted water would advise getting someone in ASAP who knows what they are doing to clean out and inspect boiler for any damage, take FGA etc, the condensate baffle is possibly perforated so all/most of the condensate will flow into the bottom of the boiler.

What is the flexible hose in the boiler flue for?. (post #33)

Yes bottom of the boiler is full of water. That Flexi hose goes from the air damper into flue

 

[adomas]

When we are discussing the size of a boiler, we aren’t referring to its physical dimensions. Instead, we are referring to the output in kilowatts (kW), the unit that is used to measure how much energy is output by the boiler in the form of heat. It is important to choose the right size boiler for your home because it will mean you are not wasting energy and money you don’t need.

Generally speaking, the more heat and hot water you require, the higher the output you will need, although other factors also play a part in choosing the right size.

 

[sherylryan]

When we are discussing the size of a boiler, we aren’t referring to its physical dimensions. Instead, we are referring to the output in kilowatts (kW), the unit that is used to measure how much energy is output by the boiler in the form of heat. It is important to choose the right size boiler for your home because it will mean you are not wasting energy and money you don’t need.

Generally speaking, the more heat and hot water you require, the higher the output you will need, although other factors also play a part in choosing the right size.

Hi there, yes I understand we are referring to the output in kw. As I mentioned we need 23 kw/h for ufh, 15 kw/h for radiators. 3 kw/h for DHW and 3.5 kw/h for trench, total 44.5 kw/h. If all of these were calling for heat at once a would boiler with 35kw/h output would struggle?

 

[John.g]

How are the heat loss calculations reconciled with that 44.5kw, presuming they were carried out before sizing rads etc?.

 

[sherylryan]

How are the heat loss calculations reconciled with that 44.5kw, presuming they were carried out before sizing rads etc?.

Yes all heat loss calculations were carried out before sizing Rads etc. we’ve taken out a 24kw gas boiler, 16kw & 9 kw heat pump and replaced with 35 kw boiler ‍♀

Also on another note Re expansion vessel. I have today calculated 214 litres of water in the whole of the central heating system, not counting the 310 litres of DHW. (Total water content of system with DHW Is 524 litres)

Also the PRV is lifting in the boiler releasing water into the condensate pipe.

 

[John.g]

With precharge & filling pressures of 1.0bar/1.5bar a 12L EV = final pressure of 2.92bar when system hot. (too close to the bone of 3.0 bar safety valve lift).
A 18L EV will give a final pressure of 2.29bar under the same conditions.

Check EV size/volume, precharge/filling pressures should then be checked, requires system drain down but quick test of diaphragm can be done by pressing the EV air end schrader valve with finger nail or whatever, if water issues, diaphragm failed, if air pressure (or none), requires pre/filling pressures checked.

 

[sherylryan]

With precharge & filling pressures of 1.0bar/1.5bar a 12L EV = final pressure of 2.92bar when system hot. (too close to the bone of 3.0 bar safety valve lift).
A 18L EV will give a final pressure of 2.29bar under the same conditions.

Check EV size/volume, precharge/filling pressures should then be checked, requires system drain down but quick test of diaphragm can be done by pressing the EV air end schrader valve with finger nail or whatever, if water issues, diaphragm failed, if air pressure (or none), requires pre/filling pressures checked.

This is in my firebird instruction manual, our EV is set to 1 bar

 

[ShaunCorbs]

You need a 25 l expansion vessel or the next size up eg 35l depending on what you have you can add to it

 

[John.g]

What size EV is installed??.

 

[sherylryan]

What size EV is installed??.

12 Litre

 

[sherylryan]

You need a 25 l expansion vessel or the next size up eg 35l depending on what you have you can add to it

Hi Shaun, yes that's what i was thinking.

Tonight I found a document in our plumbers manual and it states that they are using the DHW expansion vessel, I can't see how this will work as it is 10m away from the boiler on the discharge side of the pump and on the return pipe at the bottom of the cylinder.

 

[John.g]

Is this EV connected in to the COIL return at the bottom of the cylinder??.

 

[sherylryan]

Is this EV connected in to the COIL return at the bottom of the cylinder??.

Yes it is. (sorry EV just out of shot in photo)

 

[ShaunCorbs]

And what is the capacity of this one ?

 

[sherylryan]

And what is the capacity of this one ?

It’s 10 litres. I’m not entirely sure how this would work as the flow for bother ufh manifold goes through the those valves you can see in pic, but there return pipes are 5 metres away from that. The return pipe in the pic (at the top) is for Dhw only.

 

[sherylryan]

Is this EV connected in to the COIL return at the bottom of the cylinder??.

Yes it is John.

 

[ShaunCorbs]

It’s 10 litres. I’m not entirely sure how this would work as the flow for bother ufh manifold goes through the those valves you can see in pic, but there return pipes are 5 metres away from that. The return pipe in the pic (at the top) is for Dhw only.

But all of the returns are connected tbh I would say your on the limit of expansion

Are there service valves on them so you could drain and check the pressure one of them might be low / flat

 

[John.g]

Is the 12L installed in the boiler or outside it and if so is it connected to the boiler circ pump suction side or discharge side?.
Even the 12L on its own if properly charged, per firebird, precharge and fill pressures of 1bar then that alone would only mean a final pressure of 1.97bar with system contents of 214L and 2.23bar with 250L.

 

[sherylryan]

But all of the returns are connected tbh I would say your on the limit of expansion

Are there service valves on them so you could drain and check the pressure one of them might be low / flat

Sorry just checked it and it is 18L pre charged to 1.5 bar.
How does this work being situated here when I thought any additional vessel had to be close to the boiler.
Also how would this work with the radiators when there flow is in the completely opposite direction .

 

[sherylryan]

Is the 12L installed in the boiler or outside it and if so is it connected to the boiler circ pump suction side or discharge side?.
Even the 12L on its own if properly charged, per firebird, precharge and fill pressures of 1bar then that alone would only mean a final pressure of 1.97bar with system contents of 214L and 2.23bar with 250L.

It’s on the inside of boiler, but pump is on the outside. It has a hose running from vessel to firebox. Hope that makes sense.

 

[John.g]

Does the pressure gauge show 3bar with PRV lifting and what pressure is it showing when system up to temperature?.
You will see a plastic cap (like your car tyre valve cap) just in front of the EV flexible hose, just unscrew/remove (the plastic cap) and depress the needle valve briefly with your finger nail or if not with a small screwdriver and see what comes out.

 

[sherylryan]

Does the pressure gauge show 3bar with PRV lifting and what pressure is it showing when system up to temperature?.
You will see a plastic cap (like your car tyre valve cap) just in front of the EV flexible hose, just unscrew/remove (the plastic cap) and depress the needle valve briefly with your finger nail or if not with a small screwdriver and see what comes out.

System is on now, showing 1.3 bar on boiler, air comes out of vessel when needle is depressed .

Can on vessel be pre charged to 1 bar and the other to 1.5 bar, do they not have to be the same?

 

[John.g]

That other 18L EV has got nothing to do with the heating system, you have a unvented HW cylinder and that 18L EV is to take its expansion, are you sure its not a PRV (expansion valve or main TPRV) from this system that's lifting?.
Its unlikely that the boiler PRV is lifting if the boiler pressure is not exceeding say 2.8/3.0bar.

Even though you have established that the 12L EVs diaphragm hasn't failed the precharge pressure should still be checked as the boiler PRV will lift if this precharge pressure has fallen from 1.0bar to 0.31bar, filling pressure 1.0bar. OR (will lift) if the precharge pressure is correct at 1.0bar but the filling pressure is 1.5bar. So requires system drain down, also the boiler pressure gauge may be faulty, if not and PRV is lifting at < 2.8bar then PRV needs renewing.

 

[sherylryan]

That other 18L EV has got nothing to do with the heating system, you have a unvented HW cylinder and that 18L EV is to take its expansion, are you sure its not a PRV (expansion valve or main TPRV) from this system that's lifting?.
Its unlikely that the boiler PRV is lifting if the boiler pressure is not exceeding say 2.8/3.0bar.

Even though you have established that the 12L EVs diaphragm hasn't failed the precharge pressure should still be checked as the boiler PRV will lift if this precharge pressure has fallen from 1.0bar to 0.31bar, filling pressure 1.0bar. OR (will lift) if the precharge pressure is correct at 1.0bar but the filling pressure is 1.5bar. So requires system drain down, also the boiler pressure gauge may be faulty, if not and PRV is lifting at < 2.8bar then PRV needs renewing.

That makes John, I didn’t think the 18L EV had anything to do with the heating system. No the PRV valve on this system goes to a completely different discharge drain.

Would the new pump running at 1.35 bar but was at 2.1 bar cause problem, in the below clip out of instruction manual they talk at static head.

Also attached you will see systems description and the plumber gave us he clearly makes reference to the 18L EV being part of the heating system.

 

[John.g]

Can you point out exactly where this PRV (that's lifting ) is located? Also it appears that there is one EV on the CH system, the 12L one?.

 

[sherylryan]

Can you point out exactly where this PRV (that's lifting ) is located? Also it appears that there is one EV on the CH system, the 12L one?.

Yes there is only the one 12L EV on system . Should this be connected to the pump?

 

[John.g]

OK, thanks, I see that's a TPRV, normally, what I've seen is just the 3 bar PRV with the over temp protection done with the boiler thermostat at 110 to 113C.
So if this TPRV valve lifts with boiler pressure < a indicated 2.8bar, either a faulty TPRV or improperly charged/filled EV and the pressure is exceeding 2.8/3bar. Presume pressure indication is changing with system cold/hot?.

 

[sherylryan]

OK, thanks, I see that's a TPRV, normally, what I've seen is just the 3 bar PRV with the over temp protection done with the boiler thermostat at 110 to 113C.
So if this TPRV valve lifts with boiler pressure < a indicated 2.8bar, either a faulty TPRV or improperly charged/filled EV and the pressure is exceeding 2.8/3bar. Presume pressure indication is changing with system cold/hot?.

Yes the pressure is changing with cold/hot system only slightly though.

 

[John.g]

OK then, suggest noting that pressure the next time the PRV lifts.

 

[sherylryan]

OK then, suggest noting that pressure the next time the PRV lifts.

Ok will do thanks John. You said in a previous post the boiler pump is normally around .4 bar, 4m head, if this external pump is set to 1.35 bar 13.5m head is this an issue with the expansion vessel, as the expansion vessel charged to one bar allows the system a static head of 5m.

 

[sherylryan]

Ok will do thanks John. You said in a previous post the boiler pump is normally around .4 bar, 4m head, if this external pump is set to 1.35 bar 13.5m head is this an issue with the expansion vessel, as the expansion vessel charged to one bar allows the system a static head of 5m. View attachment 76721

Another question, I have watched the pump running on both the kitchen (troubled) and laundry manifolds, individually. Correct me if I’m wrong but should the kitchen manifold not run at less RPM than the laundry manifold that had 50m flow and return pipe? The kitchen manifold runs in 32mm cooper from boiler (5m) until it tees off for manifold then it runs in composite 26mm for 2 metres till it joins manifold.

Doesn’t the boiler pump only control the flow and return from the manifold and the manifold pump controls the flow and return in the manifold circuits?

 

[ShaunCorbs]

That other 18L EV has got nothing to do with the heating system, you have a unvented HW cylinder and that 18L EV is to take its expansion, are you sure its not a PRV (expansion valve or main TPRV) from this system that's lifting?.
Its unlikely that the boiler PRV is lifting if the boiler pressure is not exceeding say 2.8/3.0bar.

Even though you have established that the 12L EVs diaphragm hasn't failed the precharge pressure should still be checked as the boiler PRV will lift if this precharge pressure has fallen from 1.0bar to 0.31bar, filling pressure 1.0bar. OR (will lift) if the precharge pressure is correct at 1.0bar but the filling pressure is 1.5bar. So requires system drain down, also the boiler pressure gauge may be faulty, if not and PRV is lifting at < 2.8bar then PRV needs renewing.

It’s connected to the return ?