2 gloworm boilers in parallel both producing fault codes f25

[Anwah]

Hi have installed 2 gloworm ultracom 30hxis piped in parallel unvented system in 38mm
pipe reducing to 22mm under floorboards, have fitted a grundfoss alpha 2 pump,The boilers are wired through a warmworld boiler sequencer.This serves a large detached house with 3 floors and the boilers are mounted in a room on the 3rd floor. I am having problems with both boilers tripping with f25 on the displays. any ideas would be most grateful.

 

[kevplumb]

f25 (according to da book) flow temp rising to fast
temp difference to high

restrictive system

 

[Anwah]

Owner of the house says the boilers are faulting even when they are not operating and are using the imersion heater. I have replaced the flow sensor on 1 of the boilers to see what happened but made no difference.

 

[Andygasman2010]

It's a system fault, basically it's getting too hot too quick. Exactly what size pump have you fitted? 15/50 or 15/60 would be too small by the sounds of it. A big system like this would probably benefit from a low loss header to give a minimum flow rate through the boilers.

There's a few guys in here with some great advice on large systems, i'm sure one of them will post soon.

how about posting some photos of the layout?

 

[Andygasman2010]

Owner of the house says the boilers are faulting even when they are not operating and are using the imersion heater. I have replaced the flow sensor on 1 of the boilers to see what happened but made no difference.

That's really weird, especially on both boilers. It'd seriously doubt that untill you've seen it happen yourself.

 

[Anwah]

Will post photos as soon as i can can i just point out i am the electrician who helped the plumber install the system we have 6 similar systems that have never been a problem with. we havn`t installed any check valves in the pipe work but neither have we an any of the other systems either. Thanks for the prompt replies i have been their when the boilers have faulted but they were operational at the time, have thottled both boilers down to 20 kw each to try and stop the high temprature rise.

 

[Anwah]

We have had the gloworm engineers out to have a look and he said its a bit bigger system than he is used to ,but he was satisfied both boilers were functioning correctly.

 

[Agile]

I appreciate that you are an electrician but the whole setup seems an amazing mismatch.

You have 60 kW of boiler power, possibly in a house where just 30 kW would be adequate.

Then you have no NRVs on the boilers.

To cap it all a single domestic sized pump as used in a one bed flat.

It does not surprise me that there is a problem.

Can you turn off one boiler and close the isolating valves on the other?

Tony

 

[greemyamochop]

Low loss header if you need that much heat i would think?

 

[Biggles..]

Pump no way near big enough.

These boilers have a high resistence through the hex,if your system is large then the alpha jut won't cope.

 

[Agile]

If the system is large then the resistance will be low and the pump size will achieve enough flow.

However, in this case he has apparently connected TWO boilers on just the one pump and that immediately halves the flow rate through each boiler. Hence my suggestion he turns one off and isolates it.

Its difficult for me to imagine a house really needing 60 kW of heating.

Tony

 

[D_Hailsham]

If the system is large then the resistance will be low and the pump size will achieve enough flow.

What's the logic behind that?

 

[Beerlover]

Low loss header if you need that much heat i would think?

Good practice over good luck.

Cheers

 

[Anwah]

Hi Argile spoke to the plumber today the system has been designed for a 50kw load all calcs were done correctly. The original design included a large extension that the owner had planning permision for but he has postponed the new build for the moment. The pump is not running flat out which leads me to believe that its coping with the load its a 15/60 Alpha 2. We isolated
one of the boilers to see if this helped only electrically though, i have also
reduced both boiler outputs to 20kw each .
From what you guys have said we may add the check valves like you have sujested.

 

[looneyfitter]

Sounds like the return temps are too high so fitting the NRV's may cure that bit. When linking two boilers i would most certainly be fitting a LLH and shunt pumps or a reverse return setup.

Another idea would be to fit another pump on the return to give the cooler water a bit of a push.

I take it you have just piped both sets of primaries together?

Id the rest of the house in 35mm or just the boiler? If the rest is in 22 for eg then the heat just isnt gonna disapate/circulate quick enough.

Ignore the middle pump and setup, but a smaller version of this would have worked.