Fagor Feb 20e Boiler heating short cycling

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Hello,
I'm hoping some kind soul can help me to figure out what is wrong with our Combi boiler in our Caravan.

It's a Fagor Feb 20e, probably 16 years old.

Just suddenly it has started to short cycle on the heating. The hot water is fine.

So we switch the heating on, the boiler fires up then after a period of time it turns itself off as if it thinks it has reached its temperature. It is still actively turned on as I can hear it but it just doesn't fire up.
Then after another short period of time it fires up again and the cycle repeats.

The radiators are getting warm to touch but the room temperature doesn't get above 14 degrees as it isn't on long enough to get to target.

It seems to stay on for a shorter time as it gets warmer if that makes sense. So if the room is 10 degrees it is on for maybe 5 or 10 minutes but as it gets up to about 14 degrees it is on for maybe no longer than a minute.

The thermostat is fine, we've ruled that out.

I thought it would either be the CH thermistor or the PCB but an online plumber suggested it could be a faulty pump?

I've also read several places where a faulty diaphragm is the reason.

I got the local Site Plumber in to look and he literally couldn't be bothered even checking it. Just told me to get a new one. (nice)

Any help would be gratefully received
 
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Your boiler has what is called a twin pass, or Bi-Thermal heat exchanger, so if the HW is fine, pump is a good place to start , the pump on your boiler only runs when CH is switched on, not when HW is demanded
 
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Thanks for that, I appreciate the response.

I was about to add a few details I missed.

When this occurs the green light is solid then when the pilot comes on the orange light goes solid, when the pilot goes out the orange light goes out and the green light stays solid. (No flashing)

It threw a red light fault code once but I missed it so couldn't count the number of flashes.
Every other time, no red fault light.

The other thing is the pressure is a bit high. It's at 1.6 bar when cold and the Manual suggests 0.75 to 1. I told the site plumber this before he went. He's claiming he 'serviced ' it and has billed me £90 but he didn't adjust this which I'm a bit peeved at.
Charged me £90 then told me to buy a new boiler!

The manual suggests it is the thermistor or PCB when following the trouble shooting guide which I was hoping could be the problem as both can be resolved relatively cheaply.

Is there any way to confirm if it is the pump?
I can get a plumber friend to check if there is.

Many thanks again
 
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The other thing is the pressure is a bit high. It's at 1.6 bar when cold and the Manual suggests 0.75 to 1. I told the site plumber this before he went. He's claiming he 'serviced ' it and has billed me £90 but he didn't adjust this which I'm a bit peeved at.
Charged me £90 then told me to buy a new boiler!
forget that , you are adding a red herring, that is not your problem

The manual suggests it is the thermistor or PCB when following the trouble shooting guide which I was hoping could be the problem as both can be resolved relatively cheaply.

why are customers always so keen to say PCB, a pro that will be the last port of call,,

get a large screwdriver, switch the heating on , put the blade of the screwdiver against the pump, and the handle to your ear, you will hear if the pump is spinning, might just need freed off, wont cost anything
 
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I'll try that at the weekend for starters.
Many thanks for taking the time to reply.

I've attached the schematic from the manual which is what suggested PCB.
I'm aware it's a lazy diagnosis lol
 

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sadly all boiler manus do that, simple if 230V going to pump and it is not running, then the pump is faulty, or seized and needs freed , very common fault on caravan boilers as the CH is not used very often
 
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If it turns out to need a pump the Morco/Fagor price is extortionate...it looks like it's a standard Grundfos UPS15-50 3 speed which is available as a Worcester boiler spare at a much reduced price.
 
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Really!?
That's the same pump at about 20% of the price!!?? That's outrageous!!
 
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Hi, I'd like to post an update on this and hopefully it will give a steer on the precise problem.

I went to the Caravan today and watched the boiler for 2 hours. When I arrived it was 5 degrees inside. I turned on the boiler and it fired up for just under 4 minutes until the water temp gauge hit 80. The pilot then went out but the pump continued to run.
When the water temp gauge dropped to 60 the pilot came back on again and fired up until it got back to 80 degrees.
It continued this cycle all the time I was there. The pump continued to run the whole time.

The radiators all hot quite quickly, the return pipe to the boiler got hot quickly. The pump was red hot which I guess is because its pumping red hot water around?

In short it all seemed to be functioning exactly as it should but....

1) The temperature inside took 1 hour to go from 5 to 11 degrees then another hour to reach 14 degrees.
I switched it off after 2 hours and after a further 2 hours being off it has only dropped to 9 degrees so it's not like it was freezing outdoors!

2) The time cycles between the pilot coming on and going off were very variable. Sometimes the pilot was on for only 45 seconds, sometimes 3 minutes.
Sometimes it was off for a minute, sometimes 3 minutes.

My logic is telling me one of two things

1. The pump is either blocked or knackered so isn't pushing the water round the system, maybe it gets worse as it gets warm hence the erratic cycles.

Or 2) there nothing wrong with it and the radiators aren't powerful enough to heat the van. There's only 2 small radiators in the main room and they're both in the furthest corner from the door. We've never actually used it between October and March due to lockdown and we didn't have it the year before so there is an unknown there!

I'd be grateful for an opinion from someone who understands these things as I'm not a plumber by anybodys definition.

Thanks
 
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You're looking for around 10 to 15 degrees difference between the flow and return under the boiler...if it's greater than than the flowrates insufficient....could be a slow pump, blockages etc.
Check the radiators are balanced ie. similar temperature drops across each one and they heat up evenly.
If you've got TRVs pull off the heads and check the pins on the valves aren't stuck down.
 
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Thanks for the response.

There's no TRVs fitted.

The radiators do feel hot to the touch and are all similar temperature.

I'd guess a 15 degree difference is what I could feel because the out was too hot to hold, the in was still hot but I could hold it for 3 or 4 seconds maximum which is what the radiators feel like too.

We bought the caravan in March 2020 and spent 2 weekend in there before lockdown and I'm sure it was plenty warm enough in the 2 weekends we stayed over before lockdown
 
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If your radiators are all around 80 degrees at the flow end and say 65 to 70 degrees the other end with a gradual temperature gradient across them then they're working fine...but if that's insufficient to bring the caravan up to temp then they're too small for the heat loss.
 
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