Help please - Ancient Hot Water Cylinder/Tank and Ancient Thermostat

[butterflymum]

Hopeful @PigletJohn or someone can have a look at attached picture and attempt to assist with queries. Oil fired central heating system, with vented hot water cylinder, installed by previous owners c1980 or earlier.

When heating is on, the hot water from taps is verging towards scalding. We opened the lagging jacket this afternoon, expecting to see a thermostat strapped to the cylinder/tank so we could adjust it if necessary, but there wasn't one.

Shone light around hot press and on pipework at bottom left of cylinder/tank, spotted what seems to be a Sopac thermostat attached (rather loosely), to a pipe. If reading it correctly, it seems to be set at between 30 and 40 (assuming, but not clear, this is meaning degrees).

a) was it usual for thermostat to be on pipe rather on the cylinder/tank years ago?
b) is this thermostat likely to be serving any purpose when not attached to cylinder/tank, especially if the reading on it is implying it is controlling temp to between 30 and 40 degrees?
c) could water from taps be scalding because the thermostat is doing nothing?

I do realise a cylinder/tank thermostat should be at between 60 to 65 degrees to help prevent Legionella and not scald when exiting tap.

Thanks, in hope, for your input.

It's not wrong to have a thermostat on the return pipe near the bottom of the cylinder, but it is not modern practice. The stat ought to have a sort of strap to hold it tightly to the pipe, probably metal, with screw grippers. If you turn the knob the stat should click as the contacts open and close. You can buy a new one if you want and strap it to the cylinder or the pipe.

However

Although it's possible that the stat is at fault, it is only an electric switch and I suspect that it is not operating the system correctly. The cable might have been disconnected at the other end, or the system might have been altered.

Have a look for a motorised valve near either the cylinder or the boiler. Here are some examples. Please photograph it, and where the cables go.

www.screwfix.com/search?search=Port+valve&brand=drayton|flomasta|honeywell_home

And here are some cylinder stats

www.screwfix.com/search?search=Port+valve&brand=drayton|flomasta|honeywell_home

Ooops, no, here.

www.screwfix.com/c/heating-plumbing/cylinder-thermostats/cat831450?cm_sp=managedredirect--plumbing--cylinderthermostat

Quick thank you so far.....your input is appreciated. Will hopefully have more time tomorrow to do the checks and get back to you.

For tonight, turn it down to the lowest number. Does it click? Does the HW stop getting hotter?

A bit later than intended....

Stat doesn't feel/sound as if it is clicking when turned. Only just had opportunity to do it and need to go out again, so can't tell yet if any change at tap as obviously the water in cylinder is still hot.

As for rest:

No obvious sign of a motorised valve in either the hotpress or on any pipes leading from boiler casing in outside shed.

Pictures below show set up in hotpress:

I can see your system is very old. Might be 40 or 50 years or so. Can you see a pump?

Looking at the pipes from your boiler entering the side of the cylinder, they might be 28mm diameter. Can you measure them please. This would suggest it is, or was, gravity feed to the cylinder (natural convection from the boiler). To avoid the cylinder getting scalding, turn down the boiler thermostat.

It is possible to fit a thermostatic cylinder control valve, but they are hard to find and expensive. Depending what else we find, I think you would do better to convert it to fully pumped with a motorised valve. A wrinkled old plumber or heating engineer will be very familiar with this job, ask around for local recommendations. There will be plenty of people ready to sell you a new boiler, if that is what you want.

There are signs of leakage on and around the copper pipes. You can clean off the limescale and corrosion with a green nylon pan scourer and water with WUL, polish off with an old vest. Do that please. You will then be able to see if it is still leaking if the marks come back. If the pipes stay clean, the leaks have been sealed with scale.

If you are having any plumbing work done, I strongly recommend having a Magnaclean fitted. Your system is pretty sure to be full of dirt and sludge, this will trap anything circulating in the water and prevent it forming a blockage. It can alo be used in conjuction with chemicals to carry out an easy DIY clean before it gets worse. Any plumbing work will disturb the dirt and the sludge and send it round the pipes.