Boiler not fully firing so only luke warm water from boiler?

[jonnyz]

I have a Ravenheat 820/20T boiler that is outputting only 13 to 16kW on domestic hot water, whereas its supposed to do about 23kW. This means the hot water isn’t hot enough for the wife’s shower, especially in the winter when the incoming water is a bit colder.

I’ve checked the voltage at the gas valve's modulation/solenoid coil terminals and when in domestic water mode its either 0V or 24V depending on the position of the DHW thermostat. I guess it doesn’t do continuous variable control as it won’t do anything other than 0V or 24V. Maybe it should since it has a thermostat dial.

Curiously when in central heating mode it only reads either 0V or 12V depending on the position of the CH thermostat.

From this I guess the boiler does lo-mid-hi fire mode 0V-12V-24V.

At 0V across the modulation coil it heats 6.5litr/min from 10C to 40C (13kW)
At 24V across the modulation coil it heats 6.5litre/min from 10C to 45C (16kW)

I have no idea what it’s heat output is in central heating mode, but it keeps the house warm enough. The flame height seems no greater than in DHW mode.

I’ve adjusted the fuel pressure gizmo on the end of the modulator coil and sometimes get 50C out but not consistently. I may need to put the setting back however as the pilot seems to go out since. Guess it’s lifting the pilot flame off its burner.

I’ve checked for heat exchanger performance by measuring flue gas temperature, it reads 150C, that’s about normal for a non-condensing combi so my heat exchanger shouldn’t be fouled or blocked as I’m recovering all the heat.

Since I don’t get full output even when 24V on the gas valve I assume the fault is with a component associated with it. Or a fuel pressure / restriction issue.

Anybody suggest what the problem might be?

 

[bengasman]

Illegally installed by cowboy who used the wrong gaspipe would be my first guess.
What does it say on the benchmark sheet?

 

[jonnyz]

Thanks for the suggestion bengasman, looks like a good one. Just tested the pressure around the circuit with a ribena+hose manometer.

Static i've got 22mbarg just like it says on the gas meter regulator.
Dynamic it drops to 10mbarg at the inlet to the gas valve and 7mbarg on the outlet to the burner.

Two problems, almighty big pressure loss in the fuel supply. Fuel system that i can see has standard 5/8" OD copper, not sure route it takes but probably 10m+ length. Maybe fuel filter blocked due to not cleaning crap out of new gas mains.

Also at 7mbarg i should be getting much more oomph, about 21kW according to the manual. Possible restriction in nozzle/burner?

Any suggestions, maybe 5/8" is too small for the system. Although i reckon you'd need 70metres of length to cause 10mbar loss, so possibly not.

Cheers.

 

[bengasman]

Static i've got 22mbarg just like it says on the gas meter regulator.
Dynamic it drops to 10mbarg at the inlet to the gas valve and 7mbarg on the outlet to the burner.

Two problems, almighty big pressure loss in the fuel supply. Fuel system that i can see has standard 5/8" OD copper,

That boiler must be at least turned off; If I had been there, I would probably have disconnected it.
It is dangerous, get a RGI in to sort it out. I would strongly suggest that you stop tinkering with it yourself, it is bad enough as it is.

I don't think I have ever seen 5/8 pipe, it is probably 22mm.

 

[jonnyz]

Just trying to diagnose it before i get someone in, I haven't actually changed anything. I don't want to get someone in to fit a new gas valve or boiler if what i need is the pipes changing.

Quite concerning if you say the system is dangerous, maybe a daft question but how is a restricted inlet pipe dangerous. Supply pressure for the time being atleast is still well above minimum.

The pipe has 15/16mm OD, i'd consider changing to atleast 22mm if i could be sure it wasn't just a pipe/filter blockage.

Appreciate the advice.

 

[bengasman]

Just trying to diagnose it before i get someone in, I haven't actually changed anything. I don't want to get someone in to fit a new gas valve or boiler if what i need is the pipes changing.

Simple solution: hire somebody to repair the boiler as opposed to getting someone to have a look, change a part and see what happens.
Good RGI's work on no-cure-no-pay basis. You also run a good risk that a good installer will not bother to come around if the customer tries to tell him how to do his job. At the end of the day, you will kick up a fuss when it comes to paying if he follows your lead and the boiler still doesn't work.

Quite concerning if you say the system is dangerous, maybe a daft question but how is a restricted inlet pipe dangerous. Supply pressure for the time being at least is still well above minimum.

Nope, absolute minimum is 14 mbar dynamic, and that is only if all factors outside your influence are at minimum, and then only for a limited period of time. Your installation is way beyond acceptable, and has to be condemned. Faulty pipe can cause flame failure resulting in a gasescape.
The only thing I can not see from here is whether it is a matter of condemning the boiler only, or take out the meter.
Yours is clearly a cowboy job, and likely to have more problems that can be dangerous, like gasleaks, fluegas coming inside, safeties not working properly.

The pipe has 15/16mm OD, i'd consider changing to atleast 22mm if i could be sure it wasn't just a pipe/filter blockage.

Sounds like 15mm. Imperial copper was phased out decades ago.

 

[jonnyz]

Cheers for the advice.

I'll cerainly get an RGI in if its a boiler issue. I'd only tell him symptoms, not cure. Agree, that's his job.

If its a pipe issue, my father is a gas fitter with 40years experience so i wouldn't want to waste the RGIs time.

I can't fault the boiler itself it seems to be doing the best it can with the dodgy gas piping and the meter regulator is doing its job, something inbetweens screwed and i don't know what. Not sure an RGI would be interested in my problem having said all that, probably nothing in it for him??