Ideal classic ff250 tripping out on HW only

16 Mar 2015
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United Kingdom
Looking for some help with my Boiler/hot water.
Got an Ideal Classic ff250 its over 15 years old but been very reliable, problem is the boiler overheat trips out but only on hot water - all ok while the heating only or heating and hot water is on.
Tried a new thermostat on the hot water tank and motorised valve but no better, pump seems to run ok and no problems with the cold feed from the F&E tank.
Started cutting out every few weeks then 2 or 3 times in a week then back to every couple of weeks, very random with no obvious pattern.
When it cuts out there is some loud banging and clanking of the pipes in the airing cupboard and the vent /overflow pipe to the F&E tank gets red hot.
The boiler is in the garage while the hot water tank, motorised valve and pump etc is upstairs in the airing cupboard
Really appreciate any help.
Cut out again on HW this morning after about 10 minutes, not sure if the boiler trips before or after the banging of pipes and venting in the airing cupboard because it's so random. The pump continues after the boiler has tripped.
Unfortunately I am not working at the moment so looking for an 'easy fix' (if only) before calling the cavalry in !
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Easiest fix! Is to bleed any air from the cylinder coil, there might be a bleed point on top of the coil connection, about half way up.
May be there's a balancing valve that is turned (almost) off.
It most likely is a bit more challenging! Possibly a blockage, I would suspect its a "gravity to pumped" conversion and the cold feed, from the f&e tank to the system is still connected to the return of the cylinder whereas it should have been moved to before the pump, and has now silted up.
Thanks for the reply,can't see a bleed point but will take a better look later. The system hasn't had any changes to it for many years and was fine until recently.
We live in a hard water area with loads of limescale,the system has had its share of cleaner and descaler over time.
Will let you know how I get on later, thanks again
Photo of the cylinder and surrounding pipework often helps. Limescale shouldn't be an issue as the heating system circulates the same water constantly, it only gets changed if the system is drained and refilled.

Sludge is more likely, cleaner and descaler fine, but was there any inhibitor added when the system was refilled?
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Think i'm gonna try some sentinel x800 and run for a few days (will study the instructions before use)
Had a good read up and it sounds like it will at least clean some of the crap out, which can't hurt - can it ? With the problem being only random on the HW it's not totally blocked with sludge or silt.
Is the HW side of the pipework seperate from the CH because with the latter working ok seems strange, where would the silt / sludge collect ?
Whenever i've decorated I have removed the radiator in that room and flushed it out with a hose pipe in the garden, so has had an occasional 'clean'
May also try and get a picture but not a lot of room to manoevre in the airing cupboard ! Perhaps a diagram?

Sounds like boiler thermostat ..........I woukdnt be doing diy with x800 or youl be replacing rads in 3 months as well
Hi Middlesbrough

Do you reckon it could be the Boiler thermostat with it only cutting out on the hot water ?

Are you familiar with the ff 250 ? Would that be the thermistor that fits into the heat exchanger and NOT the overheat thermostat.

The piping and pump does get Very hot when operating.

I was at one today took a stat with me and potentiometer expecting to swap them . When I dropped the panel down the stat wasn't even plugged into the pcb .

The fan was replaced recently it looks like the basically hadn't plugged it back in when working on it .

£36 for that stat if replaced
Thanks I will look into the Thermostat but as i mentioned previously the only time the boiler cuts out is when the HW only is on.

It has never cut off during CH only or CH & HW together. So is it likely to be the Thermostat ?

But as a DIYer its not safe for you to open the combustion chamber cover! That needs to be done by an RGI.

What happens when you turn down the boiler temperature control knob?

Have you checked that the flow and return are correctly piped and the flow connection is the one that gets hottest?

Hi Agile

I have tried all positions on the boiler temperature knob over the past few months since its been tripping (from 2 to 6) to no avail.

The system layout has not changed for many years so i assume all is connected properly.


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