typical noisy central heating problem

hiya folks just a quick question

the problem i have has been going on for years, but i thought its time to sort it out once and for all, the way im going to explain things is going to sound really stupid but im no plumber by any means, so sorry in advance if i say some silly things

well we have a boiler in the garage (potterton flamingo 50s - 24years old) and a tank up in the loft, when we turn the central heating everything is fine, when we turn the hot water on thats when the problems start, theres a smaller seperate tank on a shelf in the loft and thats where we get a terrible noise from, it sounds like the water is boiling like mad thats the only way i can describe it, we've also had water either overflowing or being spat out of this tank

i have been told its an airlock, also i have been told to change the pump by the boiler

about a year ago we had the larger copper tank in the loft replaced but the problem was there before and seems the same now

any answers on what could be making the smaller tank make noises like it does, oh and also how easy it is to replace a pump (like any special tools or sealants) will be greatly appricated.

sorry for the long post

cheers

Could be boilerv stat out of range or possible blockage in circs is it gravity or fully pumped?

i think its gravity fed but im not 100% sure, another guy at work told me to turn all the hot taps on in the house, then close them starting from downstairs working my way upstairs, i did this let the water run for a couple of minutes then started to switch them off, i noticed that from some of the taps the water started spluttering then returned to normal.....just going to see if thats made a difference

Do you have any motorised valves?

Does the symptom occur when you select Hot Water and Central Heating, or just when you select Hot Water?

BTW, ditch the guy at work - he's talking nonsense.

not sure about the motorised valves (thats how little i know about the central heating system) it only happens when we put the hot water on

i think itll be best if i called out a plumber because i cant give you much information

In the airing cupboard, do you have anything that looks anything like this:

no not seen anything like that in the airing cupboard, or anywhere else in the house

As weareleeds observed, it's likely to be the boiler stat. You need a CORGI registered heating engineer.