Central Heating SOS

[dmh]

Hi Guys

I have a problem with my Worcester Junior 28i/ Central Heating system. Its a tad long winded so i'll try to edit it down.

I have one stone cold radiator (6 in total on system) and the rest of the radiators are only getting luke warm.
I have removed the cold rad and flushed it through and it runs clear. The TRV operates when the rad is off the wall also.
All rads have been vented and the system filled to correct pressure.
The boiler is only firing for 45 seconds and then turning off which i assumed was the boiler indicating it was up to temperature.

After this i decided to call in a Worcester approved contractor (I'm just a thick Electrician ).
The guy who came out initially changed the pump however this did not work so the old pump was reinstated. He also checked the overheat sensor and flow sensor.
He now believes that there is small blockage somewhere in the system (heat exchanger of pipework) as the flow is getting very hot very quickly then the boiler is shutting down.

He has injected the system this morning with a boiler descaler (aqueous logic) in the hope of disturbing the blockage. Since then the has been a loud gurgling sound as thoough its moving around the pipework.
Failing this working he has suggested a Sludge disolving chemical before ultimatey ripping the boards up.

Does this sound right? The guy seems an honest bloke i am just looking for others' advice.

Sorry for the longwinded post i am just very keen to get it sorted out ASAp as we have a 4 month old little girl and the house temperature is sitting around 14 degrees

Thanks in advance

Dave

 

[Billy Bob Bob]

has the thermistor been replaced?

 

[dmh]

Not to my knowledge, no! No parts have been replaced (or i certainly havent paid for any).
Does the thermistor sense the temp of the water going out?

 

[Billy Bob Bob]

yes it does

 

[dmh]

Great stuff, certainly makes sense! I will look into it and speak to the guy. Could there be any other possibilities?

 

[Billy Bob Bob]

well you have tried the pump and o/h stat,does it lockout or just shut down?

 

[dmh]

It just shuts down. It then attempts to refire after a few minutes.I have powered the boiler down at the spur, then powered up and it immediately fires so i assume that there is a time delay in how often it will fire within a certain period of time? Approx 3-5 mins between ignitions.

 

[Billy Bob Bob]

thermistor would be my first suspect ,think i would be inclined to gas rate the appliance as well put this to him see if it helps

 

[aggis]

When you removed the rad was the water black?
If the flow's getting v hot quickly, it sounds as if he's right.
Flushing might work, but may require powerflushing with a stronger cleanser. Only worth doing if you can get some heat at all rads, if not you'll have to have pipes cut out & renewed.
Once system clean & working fit a filter to protect system/

 

[dmh]

Gasman - You are a Gentleman and a Scholar. I will speak to him first thing in the morning. I will update you as and when. Thanks again!

 

[dmh]

When you removed the rad was the water black?
If the flow's getting v hot quickly, it sounds as if he's right.
Flushing might work, but may require powerflushing with a stronger cleanser. Only worth doing if you can get some heat at all rads, if not you'll have to have pipes cut out & renewed.
Once system clean & working fit a filter to protect system/

Yes the water was black when the radiators were removed. There was no sludge so to speak of though?!

 

[RoryD]

On sunday I was called to an old knacker of a boiler, a glowworm economy which was doing just this but with added banging and crashing b4 tripping out the pilot. The pipework and heat exchanger were chocker with sludge (solid) as i checked the pipework next to the CHB with my magnet (good ol' pull on it). I administered Fernox F3 cleanser and instructed the customer to leave the system on all the time. the boiler stat was turned right down and wouldn't fire as the heat was concentrated. Back to day expecting to get a foot pump on it and move the blockage on and found it was up and running since yesterday!! Point is Fernox can be used without the boiler firing but the pump running and is capable of clearing blockages

 

[Billy Bob Bob]

i am not saying this is not a corrosion issue,it could well be but i would be looking at a thermistor first i have had a ferroli and a alpha today with this type of fault it was a thermistor in each case the alphas system was spotless the ferrolis had moderate black crap

 

[PlumbingSucks]

gas man how do you check a thermister is working correctly. Do you check the resistance? if so do you look for the same values on all or is each boiler thermistor different?

 

[Billy Bob Bob]

all are different so having the values helps i do one of 2 things either try a new thermistor(they are cheap,and i keep the common ones in stock) or look at mi,s

 

[dmh]

I have just got home from work, I plan on 'linking out' the Thermister by basically disconnecting the two cables and joining them i effect bypassing its role. (I'll only do this for a matter of minutes to prove/disprove if it is the thermister) Before i do so, would anyone know which is the correct Thermister for Central Heating on this particular boiler (Worcester Junior 28i circa 2003). I have looked online but am unsure. Are they colour coded?

Thanks

 

[fuzzy]

oh let us know,LET US KNOW

 

[wnjswozo]

rule of thumb if you get restitance tnen ok

 

[wnjswozo]

meant to add 10/20 ohms

 

[aggis]

Hi, don't short it out it won't work!! Check you MI for thermista, but think it's makers part
8 716 142 302 0

Most thermistas are 10-14 k/ohms at room temp

 

[dmh]

Hi, don't short it out it won't work!! Check you MI for thermista, but think it's makers part
8 716 142 302 0

Most thermistas are 10-14 k/ohms at room temp

Whats the reason it wouldn't work? Are they not a normally closed contact which open when they overheat?
I haven't brought my bloody meter home with me

 

[dmh]

Alternatively, if i swap over the cables from the DHW Thermister to the CH Thermister would that then mean the HW wouldnt work if it is the thermister thats goosed? Or, are the seperate altogether?

 

[dmh]

Anyone?

 

[Billy Bob Bob]

worth a go for testing reasons not bound to work and do not run it like this

 

[dmh]

Cheers Gas man. I have swapped over the CH and DHW cables to stats and still have hot water. Does this mean i can eliminate the Thermister? I havent had the meter on it to test for continuity however.
The aqueous logic boiler descaler has been in the system for a day and half now and apart from more gurgling there has been no change.
Floorboards up the next step or would injecting a sludge chemical be advised?