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[Sir Tigger KC]

Hi All,

As per title and just as the weather is going to get chilly!! 

Its a Potterton Profile 80 conventional boiler.  The heating isn't coming on either on the timer, manually on the controller or the thermostat..... However, the the boiler runs fine when the hot water is switched on, either by the timer or manually.  But here's the thing! When the boiler is running and heating the hot water tank, the radiators are getting hot as well!!

I was thinking that the PCB was knackered but the rads getting hot when the hot waters on has confused me!!   

Any ideas Peeps?? 

[paul.lovejoy]

we have just had something similar on a job and it turned out to be the pump
may be worth checking ,if the pump is too hot to touch or you cant feel the vibration or adjust the speed it could be that. I will ask our plumber tomorrow/today

[feeutfo]

Loopy control unit?

[Osprey]

Doesn't sound like PCB to me - the PCB doesn't know or care whether it is being called for heating or for hot water.   Could well be the motorised valve on the central heating side jammed part way open. 

The way it should work is the timer and room stat provide power to open the valve.  When the valve is fully open it hits an internal micro-switch which in turn feeds power ("call") to the boiler requesting it to fire up.  If the valve never opens fully, there will be no signal to the boiler to turn on.  But when the boiler fires up for hot water, there will be accidental flow through the partially open CH valve. 

You can test this theory by locating your central heating motorised valve and operating it manually using the skinny metal lever sticking out of the base of the valve head.  The motorised valves will be somewhere near the main wiring box, and look like one of these



It is frequently the motor part of the unit that fails rather than the actual valve, in which case you can swap in a replacement motor unit without touching the actual plumbing, assuming you are electrically competent.  Otherwise it will be a drain down to fit a complete new valve. 

This assumes you have a separate two-port valve for CH and DHW ("S-plan"). 

[SIR Philbutt]

Doesn't sound like PCB to me - the PCB doesn't know or care whether it is being called for heating or for hot water.   Could well be the motorised valve on the central heating side jammed part way open. 

The way it should work is the timer and room stat provide power to open the valve.  When the valve is fully open it hits an internal micro-switch which in turn feeds power ("call") to the boiler requesting it to fire up.  If the valve never opens fully, there will be no signal to the boiler to turn on.  But when the boiler fires up for hot water, there will be accidental flow through the partially open CH valve. 

You can test this theory by locating your central heating motorised valve and operating it manually using the skinny metal lever sticking out of the base of the valve head.  The motorised valves will be somewhere near the main wiring box, and look like one of these



It is frequently the motor part of the unit that fails rather than the actual valve, in which case you can swap in a replacement motor unit without touching the actual plumbing, assuming you are electrically competent.  Otherwise it will be a drain down to fit a complete new valve. 

This assumes you have a separate two-port valve for CH and DHW ("S-plan").

Totally Agree - pump will go on and off with adjust of thermostat to check it

[Lazydocker]

Pump or 3 way valve

[freecall666]

check the termostat we had fault with ours last year and it was that, could here it click when moved it but heating would not come on, so got spare one out and replaced it, heating worked then.

[paul.lovejoy]

ditto what you boys are saying about the motorised valve the job we are doing is very similar and i thought it was the valve at first but the plumber thinks it is the pump we wil find out this morning when he carrys out the work could be pump and valve

[Marks DTM Calib]

Its not the pump as the overheat trip on the boiler would have kicked in whilst heating the water.

It will be the valve, either the micro switch or the motor.

You have to remember that neither the timer nor the thermostats directly actuate the boiler, this is triggered by the valve. The sequence of events is the timer calls a demand, the stat confirms its requried, the vlave moves to the correct position which in turn closes a micro switch in the valve to call for the boiler to fire.

[Auto Addict]

Its not the pump as the overheat trip on the boiler would have kicked in whilst heating the water.

It will be the valve, either the micro switch or the motor.

You have to remember that neither the timer nor the thermostats directly actuate the boiler, this is triggered by the valve. The sequence of events is the timer calls a demand, the stat confirms its requried, the vlave moves to the correct position which in turn closes a micro switch in the valve to call for the boiler to fire.

As the man says

[Sir Tigger KC]

Thanks for the answers 

The heating came on fine this morning, nice and toasty!! 

The pump is whirring away nicely and while it's hot to touch, it's not red hot.  I did wiggle the little lever on the motorised valve last night so maybe I freed it up..... 

I'm wondering whether to flush the system with a chemical cleaner like Fernox or Sentinal? Might be some crap floating about which jammed the valve?   

Thanks again!! 

[millwall]

just done mine  chemicals in 2 weeks ago  and powerflushed the system this morning  made a big difference   

[Terbs]

My Central Heating packed up yesterday...thought it was the programmer, but after taking the body off....no power on the live side. Traced the wiring to a Honeywell junction box...blown F2A fuse.
However, Honeywell care, as in the corner of the box is a spare fuse.
Luv ya Honeywell....up and running again...swmbo impressed...brownie points

[Marks DTM Calib]

My Central Heating packed up yesterday...thought it was the programmer, but after taking the body off....no power on the live side. Traced the wiring to a Honeywell junction box...blown F2A fuse.
However, Honeywell care, as in the corner of the box is a spare fuse.
Luv ya Honeywell....up and running again...swmbo impressed...brownie points

The question ahs to be though.......why did the fuse blow!

Its either the wrong rating and is being aged or there is an intermittent fault.....

[Kevin Wood]

I'm wondering whether to flush the system with a chemical cleaner like Fernox or Sentinal? Might be some crap floating about which jammed the valve?   

More likely to be the microswitch in the valve, IMHO. Same happened to ours, so if it's the normal controls that get fitted with a Profile I'd say it's likely. Same microswitch as the door locking motor on an Omega so I had a spare.

But.. you can normally check operation of the valve as there's an indicator somewhere on the body and also a manual operating lever. You should hear the microswitch click as it opens.

The PCB in the boiler will fail some other day day, but lives for now.