baxi105 he hw cycling

[Groovejet]

A friends baxi was causing him problems.. When heating was on and he'd turn a hw tap on.....the hot water would get hot(we'll come back to this). But when he'd turn tap off the boiler most of the time wouldnt go back to heating. Unless he'd turn tap on/off then it would kick back in.
Ther divertor was from NATIONAL HEATING SPARES and they told him they had no more in stock but send it and they would recondition it as it was in warrenty. I took it apart and the brass that connects to the by pass the non return bit wouldnt retract propally without help. Anyway hed had loads of problems with parts from ebay that were sticking etc. So naturally we thought this was the only problem.
He said there was a improvement in something or other but i noticed the hot water would cut out then kick back in ....repeatedly.
Id already checked sensing pipes for partial blockages when valve was out . So i removed the connectors from the 2 thermisters and put two test thermisters on. (connected to wiring but just sensing air as i didnt have time to fit them.
The boiler stayed on
I put the hw connecter back on the original thermister and it stayed on.
When i put the ch connector back on the original thermister boiler started cutting out again.
So it got late and i didnt have time to isolate and drain boiler. So my next step was to change out the ch thermister. Im pretty sure it isnt going to sort my cycling.
no1: existing thermisters read within tolerances when testing...4k both. which is why i dont suspect problem is thermisters, but with electronics anything is possible.
no2: I think the boiler will just cycle still due to insufficient flow or partial blockage causing boiler to cycle.
Can Anyone expand on this?
Pump was running so i guessed its between blockage in secondry hex or insufficient flow from pump?

 

[DP]

Stop kidding yourself that you are a boiler engineer.

 

[Groovejet]

Same old same old from this site.....not trying to be anybody, im a hard working guy whos been asked by his neighbour to see if i can get boiler going...And yeh i got boiler going. I never opened combustion case or messed with gas. I tinkered with the wet side. You have no reason be be unrespectful at all. Some people are living in hardship and knowing someone like myself who can put his hand to nearly everything , well need i say more.
If i did charge him..... fair do's....no problem there. But the family have just lost a rerlative and need things done now. And i'll add , from someone they can reley on and trust. You tell me whats wrong with anything about that?
Just because im asking to clarify few points above ....You go on one?
When i was in the gas industry i was on the installation team so yeh i didnt have much experience on breakdowns but give me a boiler ....it might take me twice as long as someone but i know that ill fix it guaranteed. And further more, i wont be one of these gas fitters who change out part after part until its working........No, i'll find the issue then buy the correct part. THE END

 

[ianmcd]

When i put the ch connector back on the original thermister boiler started cutting out again

The way that the boiler works is when the DHW thermistor senses what the temp of the DHW outlet is , it will modulate the boiler down, if this fails the CH or primary thermistor will cut the boiler out when it gets too hot, as you know connecting spare thermistors in mid air by-passes everything, but I do it all the time as a test, I would change the DHW thermistor and work from there

 

[Groovejet]

thankyou

 

[Groovejet]

Have you ever come across a thermister gone bad but testing correctly on dmm?? Just as the thermisters are testing correctly, i think the first time i measured they were 9k then before i went home i tested and they were 4k as i'd had heat running through boiler. Thanks

 

[ianmcd]

Have you ever come across a thermister gone bad but testing correctly on dmm?? Just as the thermisters are testing correctly, i think the first time i measured they were 9k then before i went home i tested and they were 4k as i'd had heat running through boiler. Thanks

yes many times, you can buy these for about £3 take in the cost to make , to post and to market, do you really think they are a quality item, just change it and see what happens , I change both at every service

 

[ianmcd]

Have you ever come across a thermister gone bad but testing correctly on dmm?? Just as the thermisters are testing correctly, i think the first time i measured they were 9k then before i went home i tested and they were 4k as i'd had heat running through boiler. Thanks

so how did you know that they measured correctly ? what was the temp when you measured them ?

 

[Groovejet]

Thankyou ian for your respectful input, and yes very good point i didnt take temp. As my infra red thermo. doesnt seem accurate so i stopped using it. Its brand new mind, from Plumb Center, Brand Tpi or something.
Anyway so i seen a noticable drop with temp rise from 9k-11k down to 4k. So i see your point .....i never did a accurate test......fair play my hands are up.

 

[ianmcd]

Thankyou ian for your respectful input, and yes very good point i didnt take temp. As my infra red thermo. doesnt seem accurate so i stopped using it. Its brand new mind, from Plumb Center, Brand Tpi or something.
Anyway so i seen a noticable drop with temp rise from 9k-11k down to 4k. So i see your point .....i never did a accurate test......fair play my hands are up.

Most NTCs with a stated resistance are measured at 37 degrees C, and designed to be tested as you hold them in your hand, as that is what your body temperature will be , there or about, but if you are going to measure them in a boiler you need to know what the temp is and have a chart to tell you what reading you should get at that temp

 

[DP]

Groovejet, I must have touched a nerve there

What do you think happens when you tinker with the wet side, what is the result of doing that on gas and burner. Just because you did not open the combustion chamber, is that fine and dandy then? Why not check with Gas Safe if that is fine.

Now let us get down to nitty gritty.
You remove the hot water thermistor and plug in another but not fitted to sense temperature. You do the same for CH thermistor. You run the boiler, boiler works. You fit HW thermistor, boiler works. You fit CH thermistor, boiler starts cycling.
You say you fix every boiler every time, 100%. Are you sure? No failures?

HW thermistor fitting is checking HW delivery temperature
CH thermistor is checking PRIMARY water temperature
Have you considered why the boiler is shutting down? Have you looked at the lights on the front of the boiler? Did you swop the existing thermistor and try these off the pipes?

it would be more fruitful to suggest you look at the diverter and find out how it works and if it really needed changing.

Your first paragraph. Hot water delivery is erratic. What are the lights telling you. Has the Hw demand been seen? Is the burner on? What is the primary temperature? Does the burner really need to be on? Hot water that is achieved at the tap- why is there hot watery there when tap run initially- hint, type of 105e

By the way, there are plenty other knights on white horses that have Gas Safe logo stamped on their rump. Not every gas engineer looks to see what is standing in the drive, size of the house, or adjusting the price accordingly. There are days when things go 717s up and job is a lost earner but needs completing because one feels ones reputation is on the line. Can I claim that have 100% success rate, far from it and never will as there is always a defect, a fault, a wabbly, a spin ball the will take out the stumps. To see a smile on customers face is the polish that shines the tarnishing knights armour me

 

[Groovejet]

Yes you did hit a nerve number 1.
Im not trying to be a clever sod,. The only reason i can have a good hit rate fixing boilers because i can put the time in to fault finding etc. These jobs i get arnt paid work as such. They are family and friends who know a handy guy and i also love fixing things and enjoy when i can pull someone out the crap. It is rewarding. The only time i can look at it is tea time or weekends you see.

The lights are increasing steady to 80 then it shuts down . Water from tap will reduce it temp noticably, and then burner kicks back in, raising temp once again, then cuts out again.

I havnt fitted new thermister yet. Like i said these jobs arnt my bread and butter, so if he wants me he knows he has to wait. And most ofthe time they will wait for me.

It was the guys say so to contact NHSpares to get divertor under warrenty sorted, so out of my hands.

The only thing with the Baxi divertors that has confused matters is he got a couple of spares packs over the last couple years. Well the spares were a nightmare, after many hours we relised that the plungers were not a exact match. So thinking the divertor was fixed, we still got problems, it caused alot of scratching heads.

When you said about hw there when tap run initially?? You refering to a Baxi instant?? Or just the residual heat from hex?? Sorry im lost? Baxi 105he!

Thankyou for taking time to put me right

 

[Groovejet]

Thanks Ian, thats a good trick simply using hand heat as a base for temperature as such....37'

 

[DP]

My mistake about Baxi instant

 

[ianmcd]

The only thing with the Baxi divertors that has confused matters is he got a couple of spares packs over the last couple years. Well the spares were a nightmare, after many hours we relised that the plungers were not a exact match. So thinking the divertor was fixed, we still got problems, it caused alot of scratching heads.

you get two different diverter setups depending on whether the boiler has an internal by-pass or not, they are not interchangeable, they will fit but wont work if you have the wrong one