Tepid HW & Rads - please give me a clue!

[ollski]

I should imagine that if the boiler is cuuting out before it has reached temperature then either the sensor or potentiometer (dial unit) needs replacing.
Ring up your servicing company and tell them this fault has developed as you probably need a fault finding engineer rather than a service engineer

 

[bimbo117]

i have a new control board, not yet fitted. Is the sensor or potentiometer (dial unit) on that?

 

[ChrisR]

I may have missed it - has anyone said to look for a bleed screw near the boiler pipes which go into th e HW cylinder? Muchly important.

How hot do the boiler pipe(s) get with the boiler temp knob turned right up? The flow AND return should both get too hot to put your mitt on for more than a split second!

Slightly bothered by the description of dealing with the leak on the pump... don't undo the nut pipeside of its valve or you get awful wet.

 

[bimbo117]

no mention has been made of a bleed screw anywhere...what does that do?

i can stand for a couple of hours holding onto any pipe i fancy no matter how high the boiler temp knob is turned up!

although when i did 1st put the new 3 port valve head on things did hot up when i set the control panel to HW only and the cylinder thermo to max... as i was instructed to do by the installation notes that came with it... but as soon as i switched the HW off & the CH on to test that, nothing... bolier didnt fire like it was supposed to!

i have re booted the system and its run for its usual 5 mins max before it shuts off since i was a little over firm with the pump and no huge or scary water leak so i dont need to rush & change that yet.

what does this bleed screw do, etc?

 

[oilman]

Slightly bothered by the description of dealing with the leak on the pump... don't undo the nut pipeside of its valve or you get awful wet.

As I said, "Don't disturb the pipe......". Undoing the nut might let a bit of water out but it won't be much if the pipe is kept pushed into the fitting.



The bleed screw is usually on a piece of pipe wich goes nowhere, and is from a T fitting on the pipe which comes from the top connection to the coil in the hot water cylinder. You may have a fat thing screwed to the top of the go nowhere pipe, if so that's an automatic air vent. (Their main function is to leak )

 

[ChrisR]

If the pipes have air in them, the boiler will just sit there hot until it overheats and switches off. Hence the importance of that (any!) air bleed valves. But the boiler should be hot after 5 minutes being ON! Wossgarnon? ALL the pipes only tepid?

Do the pipes go up or down from the boiler? COuld it be air in there? Look at where the pump is - could it be starved of water?

This is looking more like a boiler problem, but as above, if the beast is actually burning gas then something should get hot!

We still don't know if the pump is working. IF a boiler pipe is getting hot, then the pump should move the heat along!. Have you tried undoing the pump central screw and putting a small screwdriver in there - should feel the shaft spinning. Will lose a dribble of water.

If you can check for mains you could get to the boiler's "switched live" connection to check that it is getting a call for heat. (neon screwdriver will do). Find it by following the wire into the boiler. Then it should be marked. If there isn't a separate switched live then it's just the one "live" wire. You can also check the pump has volts up it.

When its alight, can you see big blue flames in there through the spy-hole?

 

[bimbo117]

yep, lovely blue flames through spy hole!

all i have done with pump so far is whack it as my selection of screwdrivers wont shift the bit in the middle... although i will have another go when i have got a better tool for the job!

there are pipes everywhere ... i'm sorry but i dont have enough understanding to work out where things are going from & to!

you said 'the boiler should be hot after 5 mins of being ON' - do you mean that or 'the boiler should not be hot after 5 mins...' cos the boiler doesnt get hot, it just stops firing!

when i 1st put the new 3 port valve on, when i was testing it, the water did get hot, although when i turned the water programme off on the timer switch and called for CH the boiler refused to fire and nothing circulated through the rads... mmm perhaps it isnt getting the call for heat as you suggest!

ok, so my next plan of attack will be check that pump is turning, check for air lock (not just bleed rads?), check that sys not starved of water... although header tank seems ok (but it looks disgusting filth water in it to me! all rusty & what appears to be a limescale scum on top, lovely!) and if no joy from any of that check that boiler is getting the call for CH?

ps thanks everyone!

 

[oilman]

Boiler outlet should be at least warm, if not hot after 5 mins, and probably the boiler should feel hot after 5 mins as ChrisR says. I don't recall if you said what output boiler you have, but even if it's small, imagine how hot you'd feel sitting on 17kW for 5 mins.

Which bit in the pump can't you shift? If it's the big screw, a coin and pliers will do. If you haven't got a screwdriver for the shaft end yet, take the big screw out of the back of the pump with the pump switched off. Look into the hole, and start the pump, you can then see if the shaft is spinning.

 

[ChrisR]

"'the boiler should be hot after 5 mins of being ON' "
I mean 5 minutes of the lovely blue flames stuff. It HAS to be hot somewhere!

The bit about it working - sort of - after you changed the motor, is worrying innthat it has stopped since. If it's a normal 3 pipe valve then it doesn't have to open for the HW to heat - the connection in the cylinder stat turns the boiler on.

 

[bimbo117]

ahhhh!! i think i may have found the problem!!

there are numerous wires that go into the control panel and i have found that when the boiler cuts out (in it's annoying way after about 5/10 mins) that if i give one of these wires (big black thick one that appears to feed onto the control board through a slot by the temp knob) a little waggle it refires!

it has been happily firing away now for about 30 mins and i have hot rads & hot water! its a miracle!

time will tell though... will it go back off when everything is the right temp & come back on when it gets chilly again! or will it just blow up!?!

i will let you all know!... if you dont here from its cos i've blown myself up!

 

[oilman]

So much for sophisticated professional opinions then, wonder if I should give up my day job

 

[ChrisR]

Should have suspected a bad connection - it IS a Baxi!
Could be a loose wire in a connector etc but also quite likely is a broken solder joint on the board. Often repairable.
A new board is quite expensive (check on HRPC or Boiler Spares Online site)

If you're handy with a soldering iron it can be worth resoldering joints near the edge of the board. I have one in front of me where the relay pin connections eventually vaporized.

The pcb comes out fairly easily if it's like I remember. There's a black plastic peg you have to pull out with pliers.

 

[bimbo117]

i accquired a pcb in my quest for fixing my heating a week or so ago (not yet fitted)... only cost me a £10.00 off ebay.... so hopefully that will do the job...which will be a result! Is there a permanent live on this thing i.e. am i likely to do myself a mischief when i replace the board? For safetys sake should i turn off all the power to my flat when i change it?

AND .... i'm not counting my chickens yet! So Oilman and ChrisR... dont you dare give up your day jobs! Even if this isnt the root of my problems you have all been brilliant support to me... i wouldnt have been brave enough to do what i have done without people like you reassuring me and giving me other ideas to have a go at next when things didnt work! so dont go too far away, i may call on your experience again!

 

[ChrisR]

Yes it's ever so live in there. There should be an isolator of some sort for the boiler - ususally a fused spur, or a normal plug in a socket. Just make sure it's dead!

I'm off to NZ in a couple of days - others can more than cope!