Classic FF340 low feed temperature, any ideas?

[BrianN]

I have trawled the web but cannot find an answer to this.

I'm convinced the boiler (14 years old) isn't reaching the 82c which the manual says it should and would, therefore, like an opinion on where the problem is most likely to be. There's the control knob (potentiometer) on the front and a pcb inside, I guess the gas valve is also part of the equation (and probably more besides)

The control knob is just a potentiometer but, in a recent visit, an ex-british gas plumber reckoned it was one of the most common faults along with the thermostat sensor (which I asked him to replace) - he's also got the potentiometer but hasn't fitted it yet - he doesn't want to charge a callout fee for a £10 part so will fit when he's in the area again.

I have read that the control PCBs sometimes suffer dry joints. I can get a reconditioned pcb for about £50 (with warranty) and am contemplating buying one so the plumber can fit it when he comes next.

I have strapped digital thermometers to the flow and return pipes on the boiler and recorded the temperature over a 24 hour period. It would appear that the boiler output peaks at about 65c (manual says it should do 82c) but the boiler feeds a boilermate 2000 and the store temperature rises to 73c (at times) - so a discrepancy in the thermometer readings which could be due to them being taped to the feed and return pipes - maybe.

However, the BoilerMate store temperature should be between 74c (call for heat) and 77c (satisfied). So it looks to me like the boiler isn't delivering the goods anymore.

I have recently added x800 after cleaning the CH F&E tank (full of crud) and am about to drain the system down to add x100. (Might wait till the pending cold spell has gone).

Sorry for the long post - better than drip feeding I think.

So, back to the main question, what do you think is the most likely cause of the boiler output temperature being low?

many thanks

 

[durhamplumber]

The main cause is its a rubbish boiler.The secondary cause its knackered.

 

[Hot&Cold]

The main cause is its a rubbish boiler.

really,ideal have produced some clangers but the classic f boilers are a tidy item.

 

[BrianN]

Which part is most likely to be knackered?

The estate I live on have all had Ideal Classics and Boilermates installed from new 14 years ago - I don't see loads of gas men visiting.

All the people I have spoken to in the plumbing trade reckon these boilers will trundle on for about 30 years - that'll probably see me turning off the mortal lights.

 

[ianmcd]

The Ideal Classic is a decent boiler, without seeing your system I cant really advise, you have already had the thermistor changed which is the usual culprit, your thermostat readings are not correct if the , boilermate is reaching 73 degrees, the fault may very well be with the boilermate and not the boiler.

 

[Hot&Cold]

So it looks to me like the boiler isn't delivering the goods anymore.

Has the hw tap water temperature been measured ?

 

[BrianN]

I fitted a new control board to the Boilermate two weeks ago - a seperate fault - turned out not to be the board but the digital timer going ape, so now I have a spare PCB. I have used an infra-red temp guage on the Boilermate pipework (PHE and DHW sensor after painting black) and they agree within a few degrees of what the Boilermate is telling me. The store sensor is in a black hole so I haven't anyway to take a reading from there. So, I tend to think the BM sensors are ok. I could replace them all as I have spares bought when I had a real controller pcb problem 4 years ago - I plan to flush the system soon and it might be a good time to swap them out.

The boiler temperature readings were taken by taping two accurate digital thermometers to the flow and return pipes at the boiler end. So, it's as close as I can get to the actual boiler water temperature. On max setting it should heat water to 82c.

I'm convinced it's the boiler because it takes a long long time for the house to warm up (the store temperature takes ages to rise to 73c) if I set the overnight temperature on the wall stat to 18c. For the moment I'm leaving the overnight temp at 21c - especially with the Siberian Summer coming this weekend.

All opinions will be considered and gratefully received.
Thanks for those who have replied so far.

 

[BrianN]

Old&Cold - no. Sometimes HW can get very hot (too hot for hands) but if the BM Store temp is low it won't anyway. And, all the pumps run. But why should that affect the temperature I see coming from the boiler?

 

[BrianN]

So, 10 days and no further suggestions? I'm amazed - there must be a wealth of experience out there.

For anyone not familiar with this thread my system is an Ideal Classic FF340 feeding hot water to a Boilermate 2000. The boiler flow output was below the boiler manual indication of 82 degrees - maxed at mid sixties - now it's even lower! I have been recording the temps.

About 2 weeks ago I added x800 with the intention of flushing any sludge out and just left it to run. Opened all valves on rads to ensure max flow. Last week I bit the bullet and flushed the system - set the drain rate to match the feed tank fill rate so as not to introduce air. The boiler and boilermate were switched off. After an hour and a half the water was running clear so I added x100 to the expansion tank and allowed it to enter the pipes by stopping the cistern refill long enough for the water level to fall to about 10 cm above the feed pipe. All went well.

The boiler feed and return pipes enter/exit via the top of the boiler so I'm guessing that any sludge in the boiler would not be flushed out with this technique but I also don't think it is sludged up because it was recharging the Boilermate.

I switched everything back on, opened up all TRVs upstairs - rads downstairs are controlled by wall stat so fully open anyway. Let the system do it's thing in the hope any residual sludge in the boiler would also be shifted. Everything seemed fine to start with. BM store temperature got up to 72 degrees - I did hope for more but flushing seemed the best first step.

Short lived, the boiler output temperature started to fall, at each firing, over the next 24 hours till output was below 50 degrees (I am still monitoring the flow temperature). The boiler actually fires but only for a short time (about 10 mins) then seems to sleep whilst the thing cools down.

As I see it there could be two causes.

Firstly, the classic FF340 has an overheat thermostat on the flow pipe. So, I'm thinking - if this is failing and it trips early the boiler won't get up to temperature. It would take time for the boiler pipework to cool long enough for the thermostat to kick back in and the boiler to fire again. That is the behaviour I'm seeing (about 10 minutes on and half an hour off, approx) and so I've ordered a new thermostat. At 14 years old it's worth replacing I think - especially as the boiler isn't giving the 82 degrees mentioned in the manuals.

Secondly, possibly sludge in the boiler. I can envisage the boiler temperature rising rapidly enough to trip any other temperature limit sensors (The cutout/limit is never tripped.) before the hot water gets to the flow pipe. This would have similar symptoms BUT since the hot water is getting to the boilermate (when the boiler runs) I tend to think the boiler isn't heavily bunged up. Also, when the boiler kicks in it runs for between 10 and 15 minutes before it switches off again. If the boiler were sludged up I would expect the shutdown to happen quicker than 10 minutes.

I have tried contacting an RGI (a highly recommended ex-British Gas bloke) - but he's clearly too busy to reply. He replaced the boiler thermostat a few weeks ago - but it didn't cure the problem. As the unit is 14 years old I thought it prudent to let him do that. I'd rather stick with one guy who gets to 'know' my system - anyone else who is available might be available for good reason, if you get my drift.

Please don't talk about replacing the boiler. My view, and that of many others, is that this boiler will go for another 15 years and repairing will probably be considerably cheaper.

Anyway, I'd appreciate knowlegable and helpful suggestions even confirmation that my thoughts regarding the flow thermostat being dodgy are correct.


Thanks