Boiler overheating/shutdown

[jake40]

Hi everyone,

Ihave a problem with my Barlo Balmoral boiler for past few weeks.(open vented system) Initially became noisy and then would shutdown immediately after switching it on. I took it apart and found that the heat exchanger was completely blocked with lime/deposits. A car radiator repairman cleaned and descaled it for me and for next few weeks had a perfect heating system - very efficient.
Recently however, it began overheating again. About 5 minutes after switching on, it will make a rattling, gurgling sound, then a bang and the safety switch will trip. The inlet and outlet pipe will be extremely hot. It appears as if the water is not circulating, although the only rediator which becomes warm is the one farthest from the pump! I changed the pump which did not help. A plumber came and thought the pump might need to to be changed to a more powerful one. Is he right?

 

[oilman]

A plumber came and thought the pump might need to to be changed to a more powerful one. Is he right?

NO!!!!!!

You have changed the pump with no effect. It worked ok for a while.

With these two starting points, you need to diagnose the problem, so please don't listen to people who suggest a bigger fatter 200HP pump will cure the problem. He's a merchant who can't tell you what the problem is.

(Do I sound like I have a bee in my bonnett? )

It does sound like you have a circulation problem, how old is the system?

 

[jake40]

Thanks for reply oilman - the system is 14 years old - we live is a hard water area, there was alot of sludge etc in the system but I have flushed it on several occasions over past few weeks.
The old pump was a wilo 25/60 but the current one on checking is a 25/40. would this be the problem? The house is a single story with 11 rads.
It does appear to be a circulation problem, but if the pump is not at fault, what is the next step?

 

[oilman]

If the pipes go underground, and the drain cock is above ground, you could have sludge settled in the underground part, and it would need a powerflush.

With the age of your system it seems a reasonable approach.

 

[jake40]

I think you are confirming my suspicions oilman! The pipes are underground and I have found alot of sludge, solid matter in the pump casing each time I remove the pump. I connected a garden hose with good pressure to the system today but it did not solve the problem. Tomorrow, I will try a borrowed pump and if this fails, then it has to be a blockage somewhere - I would suspect the return pipe from the rads to the pump. Thanks again.

 

[jake40]

Tried a more powerful pump this morning - no improvement: boiler overheats and shuts down after 1 minute. Power flush is the next option.

 

[jake40]

Flushed the system with an air compressor and no blockages found in the pipework. Checked the heat exchanger again and the flow is definitely slowed and this appears to be the problem. I will try again to unblock it but I may need a replacement - does anyone know if this can be got for my boiler which is a Barlo Balmoral 50F - I believe they have gone out of production.

 

[ChrisR]

Worth trying to descale it by circulating (in a short loop, ie with other rads shut off) an equal mix of DS3 and DS40. Get it warm and expect some gassing.

 

[jake40]

Thanks ChrisR - I've actually removed it and given it to a pal who has equipment he can connect it to and hopefully clean it out. Why do you think it became blocked again in such a short period of time? It was like new a month ago - would the additive I used in the water have caused it.
When I eventually get to refill the system again, which water treatment should I use to prevent limescale buildup?

 

[oilman]

The heat exchanger might just be an easy place for crud to settle as the water speed will reduce. If the blockage is on the heating side, you need a corrosion inhibitor, as lime scaling will be limited as the water does not get changed very fast. If it's on the tap side, then use a siliphos water conditioner such as Combimate from Cistermiser. Magnetic and electronic ones don't have scientific backup, whereas the siliphos ones do.

 

[ChrisR]

Just wondering if some of the scale in there has flaked off and caused a blockage. Do you know which chemical the car rad man uses? could be different scale. LIME scale isn't a problem afaik in ordinary boiler heat exchangers - only in combi secondary ones where there's lots of tap water flowing through. Scale in boiler primary h/e's is more a sort of rust, which takes a long time to form.

Scale can form quicker if your system has a fault which causes pump-over in the header tank, or a leak which means constant refreshing of water with hardness and oxygen.

If I had to bet on which inhibitor is best I'd go for Fernox MB-1, but there's no comparative info available. Sentinel X100 is the other main one rec'd by boiler mfrs, though sentinel say it should be topped up every 2 - 3 years - Fernox say 10 years.

 

[jake40]

Oilman, ChrisR: Many thanks for all the invaluable help over the past few days. Once the system is ready to be filled, I'll add the fernox to the water - was also thinking of using rainwater to fill the system.

 

[boilerbeasty]

I'd avoid using rainwater if I were you. The pH may be different due to dissolved gases (depending on air quality), and it can have a good deal of suspended particules from soot and dust in the atmosphere.
If you're putting inhibitor in the system, just use tap water and let the inhibitor do its job.

 

[jake40]

Ok - So I should go with tap water and Fernox Mb-1 when I get the heatexchanger back today (hopefully!). Will keep you posted.

 

[jake40]

Got heat exchanger back yesterday - says he sound a "spring-like " device which was partially blocking the outlet pipe. Thought it might be used to regulate the flow of water through the exchanger. System is not working fine again. Thanks for the advice over the past few days - I've learned alot about my own system