Ideal Concord WCF 55 Boiler?

I have the above boiler and it runs fine except i have a feeling that the theremostat may be starting to play up.
I put a new one in about 10 yrs ago,but as the boiler is about 25 yrs old any help in identifying a replacement theremostat would be most grateful.
I do not wish to install a new boiler but there must be a universal thermostat available!
Any help would be most grateful.
Thanks Rich.