Boiler Situation - cause?

[SirLancelot]

Main Combi 25 Eco

There is no system filter. 3 rads - whole install (pipes & rads) were new at the time. About 8 yrs old. Hard water area.

Central heating can be on for hours - no real issue. But, If I then turn thermostat off - as I am going to have a shower - and turn the shower on (hot) - the shower starts warm, but, after a few mins it goes totally cold and I get - E110 on boiler and it locks out. The boiler temp gage climbs to 88-90, then starts coming down over time.

If I leave boiler to cool down long enough - central heating can be used again with no issue.

Can fellow members give me an idea of the likely problem & scope of works - so I can make an informed decisions - when any options are presented to me.

(I am not gas safe registered - and wont take any risks - so will be seeking a specialist that can address this. I'm looking for any specialists in middlesex (london) to reach out and give me some quotes to start work asap. I have been taken advantage of by tradesmen before - caught red handed - this is why I always explore problems here first).

 

[CBW]

Hard water area I would suspect a blocked plate heat exchanger. All other taps ok?

 

[Madrab]

Yup, sounds like the plate needs descaled.

 

[SirLancelot]

Yup - only issue is when hot water is turned on. Funny thing is that the hot water pressure is good - but cuts off after about 4/5 min.

So basically it looks like the PHE is clogged/scaled up.

Could it be the thermistor? (Because CH can work for hours without issue - does that help rule it out?)

 

[Madrab]

Yeah, the boiler isn't overheating on CH mode, only on HW? That suggests that the Plate can't transfer the heat into the cold water quickly enough and the boiler then overheats and locks out. In a hard water area then that's typical of a scaled plate HEX.

 

[SirLancelot]

Makes sense.

Given that it's likely blocked & there's no system filter - is it more likely being scale or CH sludge or both?

 

[Justin Passing]

More likely the heating side from what I've cleaned, though I have a renter near Epsom where the water blocks a lot of things up it's so hard, and it scrapped an old boiler. The later boiler has been OK.

You don't need to be a gas man to do this and you can clean the plate heat-exchanger. You won't need a new one, they're very cleanable. Total half an hour with ease once you know the hazards but you can still get yourself into a mess with water if you're unprepared. Any valve you use is more or less likely to leak, water on the electrics could be expensive, etc.
It could be something else as well, but you need to know the "plate" is clean first.

 

[SirLancelot]

More likely the heating side from what I've cleaned, though I have a renter near Epsom where the water blocks a lot of things up it's so hard, and it scrapped an old boiler. The later boiler has been OK.

You don't need to be a gas man to do this and you can clean the plate heat-exchanger. You won't need a new one, they're very cleanable. Total half an hour with ease once you know the hazards but you can still get yourself into a mess with water if you're unprepared. Any valve you use is more or less likely to leak, water on the electrics could be expensive, etc.
It could be something else as well, but you need to know the "plate" is clean first.

I think i'll have the gas safe chap remove the plate and refit it. I don't like touching the boiler myself, as it's in the family house. Any small error - could have serious consequences.

However, once he hands me the PXE - can you help me understand how to clear it out? What would I need? What would I need to do.

 

[muggles]

If you're getting someone in to remove and refit it you may as well have them clean it too. They aren't going to stand around for free waiting for you to do it, and should have the proper equipment to do the job in a faster time than you can. Given that a replacement heat exchanger can be bought for around £30 though, I personally wouldn't be fannying around trying to clean it. It'll cost you almost that much in chemicals to clean your existing one when you could have a shiny new one instead

 

[ianmcd]

Total half an hour with ease once you know the hazards but you can still get yourself into a mess with water if you're unprepared. Any valve you use is more or less likely to leak, water on the electrics could be expensive, etc.

Please explain how you do this and what is this valve you speak of

 

[SirLancelot]

Question:

What signs would You look for to rule out - a diverter valve failure/malfunction.

(CH can be on all night - no problem. But when the kitchen sink hot-water/shower is turned on - the water is hot for a few minutes - then all of a sudden it goes cold. The boiler has locked and the temp gage has climbed high. Error E110. At this point CH will not turn on. But, If left for a significant time to cool down, the CH can be switched back on - and will happily run for hours, without issue).

 

[ianmcd]

you need to replace the plate heat exchanger

 

[SirLancelot]

Thanks for your guidance. It's genuinely appreciated.

The PXE needs replacing. Agreed. To be Actioned. Consider it done.

I'm asking fellow members of the community - that once this is done - is there any chance it could still be something else - e.g diverter valve.

If so - before the PXE is swapped (i've decided that if the origional PXE lasted 10 yrs - a new one (£30) will last past the lifetime of the boiler).

I will be swapping a NEW one out - and will clean the origional one out myself - ( to be retained as a backup) - should the situation repeat in the near future.

So now that we have cleared up whats going on.

KEY QUESTION:Is there any chance this situation has something to do with the diverter valve? If yes - Why?

The problem only occurs when I turn on a hot water tap. No other time.

 

[CBW]

Get the engineer to check the Diverter when there, but I’d say it’s fine. Do the radiators heat up when using the hot water?

 

[SirLancelot]

Get the engineer to check the Diverter when there, but I’d say it’s fine. Do the radiators heat up when using the hot water?

Nope - it's one or the other. But when tap is opened - boiler locks out after a short time.