Intermittent hot water Optima 901

[Neil Carroll]

Ongoing issues with boiler , I require a few answers to a few questions please , it would be great help , going through a process of elimination.

Heating seems ok , however water gets hot , runs hot for a few minutes then goes cold , then starts to get hot again . I've changed the thermo on the hot water pipe , didn't make a difference.

To help me narrow it down .

If the CH cuts out every now and then due to overheating in a similar way to the water ( I wouldn't necessarily realize it as boiler is in another room ) , if the CH thermo is faulty ( I didn't replace this once ) would CH cutting out effect Hot water also , would both cut out as a fail safe if the thermo on the other kicked in ?

Thought might be worth changing CH thermo if this is a possibility .

Second question is would a faulty flow valve result in on off hot water or would it prevent water heating at all .

I knows it possibly heat exchanger , however I want to eliminate everything first.

 

[cross thread]

It could be the gas setting on your boiler but this needs the correct equipment to set it up,

 

[DP]

Get someone who knows the boiler
You are looking for a needle in a haystack. Proper procedure is required to nail this one down. That boiler, or any boiler, must be serviced as makers intended before any remedial work can be carried out.

Fortunately this boiler diagnoses is easy the way it is made

 

[Neil Carroll]

Thank you all , I appreciate the advice , you may think that I am ignoring some of you but I am taking it all into consideration .

Following on from some advice I swopped the wires so that the hot water sensor wires were on the CH thermo and the CH sensors were on the DHW thermo

I discovered this as a result , ( I've swapped them back since !) When hot water wires were on CH feed thermo the hot water was constantly at the same temperature , I couldn't really comment on CH as I didn't have wires attached for too long ,

So now I'm thinking that it was thermos all along and the new one that I put on the DHW feed was a dud , does this make sense as when wires attached to DHW pipe water is at a constant temperature?

 

[MeldrewsMate]

To what item do you refer as a 'thermo'?
At what constant temperature was your DHW after you swapped the 'thermo wires'?
The one common element to your original symptoms is the main heat exchanger. You may need to get an RGI in to flush/clean it, and the rest of the system if that is needed. Also...

If the CH cuts out every now and then due to overheating in a similar way to the water ( I wouldn't necessarily realize it as boiler is in another room )...

...does this comment indicate that you haven't done any investigation yourself before posting for help? It would be unreasonable to expect anyone else to help if some basic data hasn't been provided by you?

Having said that, have you considered observing the gas meter whilst DHW is being drawn? If the meter register runs at varying speeds but doesn't stop then it could be assumed that the gas flame has modulated properly, rather than gone on-off. Try this at different draw-off rates such as 5 litre/minute and 15 litre/minute.