Ravenheat LS100 overheating

[MrWild]

Hi,

Looking for a bit of advice with the Ravenheat LS100. Over the recent months I have replaced just about every part on this thing and am still having difficulty although it was running perfectly at one point.

Situation is, I have a problem with the boiler overheating when the water flow-rate and demand is high.

If I open the hot water tap 3/4 of the way, the modureg kicks in, and I see the gas pressure fluctuate up and down and the boiler maintains temperature of the water.

If I open the tap fully (equivalent flow as if taking a shower). I see the modureg go up to 16mbar which is wide-open as it attempts to heat the water. About 30 seconds later I then hear the water begin gurgling as it sounds like it begins to boil and overheat, and the system shuts down, and then relights. This is resulting in hot&cold showers. To fix, I simply turn down the flow rate, and I get weaker albeit hot regulated showers.

I've tested the thermistor and it goes down to 4kOhms from 20kOhms. So looks as though it's working. I'm of the opinion that 4k is a good reading for a hot system, but should it be reading lower? Strikes me that it's unlikely to be the thermistor if its regulating the temperature at lower flow.

I suspect I have an airlock or waterlock but not sure where, there's a red bleed valve for the CH but unsure why its overheating. Clearly the thermistor is telling the system to keep the modureg wide open, so my guess is water is boiling near the overheat thermostat, any thoughts?

 

[transam]

16 mbars u say ?

 

[Slugbabydotcom]

Was one of those parts you changed a gas valve?
What other parts have you changed?

I can't give any 'gas train' related advice on here as it's against the rules unless you are gas safe registered yourself then you should register for the combustion chamber.

Otherwise give Ravenheat a ring and they might give you my number.

 

[transam]

long time no see Slug

how are you ?

 

[Agile]

Well we can see what the problem is but we don't give DIY advice on that kind of thing on this forum.

The obvious advice is to get a gas registered engineer to diagnose and repair the fault.

Tony

 

[MrWild]

Don't think it has anything to do with the gas. Think it is elsewhere.

Datasheet for the modureg states up to 16mbars, so this appears nominal.

* Regulator not changed -- min max pressures set correctly, although the max only seems to affect the manual control when the solenoid is depressed.
* Heat exchanger changed
* PCB changed
* thermistors changed a while back
* divertor valve changed.

 

[Agile]

Sounds very expensive blindly changing parts on spec!

Usually far cheaper to get a professional to correctly diagnose the fault.

Tony

 

[MrWild]

Tony, I don't see how that's a helpful contribution to the problem at hand. Your comment is not correct, or appreciated.

 

[Agile]

I am sorry that you don't appreciate my advice and that you think that its incorrect.

However, I do think that its correct and I will explain why!

The normal lowest price for new parts which you have listed are:-

Heat exchanger changed £080
* PCB changed £130
* thermistors changed a while back £020
* divertor valve changed. £100

That comes to a total of £330 ! Thats ignoring any charge for fitting them !


My expectation is that if you were in my local area then I would be able to diagnose and fix your boiler for £84.

Thats £246 cheaper that throwing parts at the boiler as you have done!

Even in the unlikely event that I did need any part then the cost would be a maximum of £130 and thats still a saving of £116.

Thus I believe that what I said was correct and I am sorry that you cannot see how calling a professional can be more expensive.

Even calling British Gas for a fixed price repair at about £300 would still have saved £30.

Tony

 

[Agile]

I expect that what you would see as a useful contribution would be to tell you what I think is wrong.

But I am prevented from doing that by the forum rules.

But after what you said above, I would now be unlikely to tell you whats likely to be wrong as you don't appreciate my ( free ) advice as well as questioning my ability.

But there is only one place to properly diagnose boiler faults and that's in front of the boiler. All I have to base my thoughts on are what you have told us.

Tony

 

[oilhead]

I assume that the system pressure is correct and expansion vessel is serviceable. If boiler pressure falls low on my boiler, I get the same symptoms.

 

[MrWild]

But after what you said above, I would now be unlikely to tell you whats likely to be wrong as you don't appreciate my ( free ) advice as well as questioning my ability.

If your only motivation is to pollute a genuine topic with otherwise worthless input, then I would have to agree with you.

Your figures quoted might be list price, but they are certainly nowhere near what I have paid. I fitted the parts myself, they were required. If you read about the legislation you'll understand that this is perfectly acceptable.

Your comments about a 'qualified engineer' are nothing more than a scaremongering sales pitch. I'm not asking your advice on what has already been done so refrain from going off topic.

Oilhead, yes the system is charged to the correct pressure, and the expansion vessel is operational and charged. I suspect the pump isn't delivering the flow rate on the CH, and thus the system is overheating when the DHW demand is high.

 

[snes]

Agile has answered you quite succinctly, and has explained why he cannot advise further.

But if it keeps you happy, carry on changing parts. You've nearly got a new boiler.

 

[Dan Robinson]

If I open the tap fully (equivalent flow as if taking a shower). I see the modureg go up to 16mbar which is wide-open as it attempts to heat the water. About 30 seconds later I then hear the water begin gurgling as it sounds like it begins to boil and overheat, and the system shuts down, and then relights. This is resulting in hot&cold showers. To fix, I simply turn down the flow rate, and I get weaker albeit hot regulated showers.

Don't think it has anything to do with the gas. Think it is elsewhere.

Datasheet for the modureg states up to 16mbars, so this appears nominal.

* Regulator not changed -- min max pressures set correctly, although the max only seems to affect the manual control when the solenoid is depressed.
* Heat exchanger changed
* PCB changed
* thermistors changed a while back
* divertor valve changed.

This load of drivel proves you lack the ability to repair this boiler. If the heat exchanger is not part of the gas train the what the flock is?

Forum rules are forum rules - you won't get advise on this repair.

 

[PEDANTICVINDICTIVEMAN]

Sounds like a faulty boiler owner, have you tried changing that ?