Oil fired Central Heating thermostat may not be working.

anotherquestion

Hi folks,

We have oil fired central heating.

Just noticed today that the radiators seem to be getting hotter than usual as well as the hot water cylinder upstairs.

Kept an eye on the boiler in the boiler house, and it didn't switch itself off within a 25 minute period.

It is an old cast iron boiler over 30 years old, the burner part was replaced about 20 years or so ago.

I do get it serviced every year, so just called the service guy, but will probably be Monday before he gets back to me.

Is it dangerous in the sense that the hot water cylinder could somehow burst if the water totally over heated and could do a lot or injury or damage, if thermostat is broken.

Thanks for any advice.

Albermarle

Is the hot water cylinder vented ( maybe fed from a cold water tank in the loft) ? If so it will not burst as the pressure can escape. However I guess there might be a lot of gurgling in the tank and the loft, so best not  let it get too hot.
If is an unvented system ( closed system ) then in theory it could burst, but these tanks have more than one safety system to release excess pressure.
The hot water tank should have its own thermostat to stop overheating ?

anotherquestion

Thanks, I think it is probably fed from cold water tank in loft, a quite a few more or less vertical pipes leading into it. Not sure if its got its own thermostat, but even if it had would the fact that the thermostat in boiler in boiler house not working still leave the cylinder thermostat more or less redundant.

I have the heating on again, but going to keep and eye on it to see if boiler stitches itself off now and again.

Just to add to this, I replaced a radiator upstairs and it has one of those thermostats fitted to it, I don't think though this should have a bearing ( or does it) as this was done about a month ago, and it is only today that I noticed this rad was a lot hotter than usual.

so my main concerns that it is the thermostat on boiler are

1 The boiler doesn't seem to switch itself off as it usually used to do.
2 The radiators, hot water cylinders and even hot water from the hot water tap seems a lot hotter than usual.

Am I right in thinking that the above points would indicate a faulty thermostat on boiler?

Many thanks.

Veteransaver

What is the boiler thermostat set to, it may have been inadvertently set to max and those old boilers will get incredibly hot, like 80/85 degrees.
I assume you have a gravity fed hot water system as a pumped hot water system will shut off once the hot water cylinder gets to the required temperature.
A gravity fed hot water system will eventually reach the temp of the boiler.

Section62

anotherquestion said:

Thanks, I think it is probably fed from cold water tank in loft, a quite a few more or less vertical pipes leading into it. Not sure if its got its own thermostat, but even if it had would the fact that the thermostat in boiler in boiler house not working still leave the cylinder thermostat more or less redundant.

I have the heating on again, but going to keep and eye on it to see if boiler stitches itself off now and again.

If the boiler (flow/system) thermostat isn't working properly then the water flowing around the system could be hotter than ideal, and that could lead to the top part of the hot water cylinder contaiing water which is uncomfortably hot.  But the cylinder thermostat should still work and stop the boiler (or 'demand' to the control valve(s)) when the cylinder is all hot enough.

In addition to the flow/system thermostat, the boiler should be fitted with a safety 'limit' stat that turns off the boiler if the system water exceeds a safe temperature - if that is working correctly then there should be no risk of explosion from the boiler, pipework nor the hot water cylinder.  If triggered the thermostat will probably illuminate an 'overheat' warning light, and might cause the boiler to go into 'lockout' requiring a manual reset before it will work again.

Section62

anotherquestion said:

Am I right in thinking that the above points would indicate a faulty thermostat on boiler?

If you have an 'S-plan' or 'Y-plan' system then a faulty control valve could cause the same symptoms.

mexican_dave

Much of the above advice is based on assumptions: assumptions there is a cylinder thermostat; assumptions the pump will stop at a given temperature. You have said your boiler may be overheating, you have a header tank in the attic and a hot water cylinder. The parts that could have have failed are the programmer, a "zone valve" of some sort, one or more thermostats. Really I think you should call out your heating engineer.

Section62

mexican_dave said:

Much of the above advice is based on assumptions: assumptions there is a cylinder thermostat; assumptions the pump will stop at a given temperature. You have said your boiler may be overheating, you have a header tank in the attic and a hot water cylinder. The parts that could have have failed are the programmer, a "zone valve" of some sort, one or more thermostats.

The OP said -

"...would the fact that the thermostat in boiler in boiler house not working still leave the cylinder thermostat more or less redundant"

mexican_dave said:

Really I think you should call out your heating engineer.

The OP also said -

"...so just called the service guy, but will probably be Monday before he gets back to me."

anotherquestion

Thanks so much for all the replies, really appreciated.

The service guy has got back to me and his advice is "a new boiler"

Taking into consideration that its an old cast iron boiler installed when house was built in late eighties, rather than putting of the inevitable which probably I have been doing, I will get it replaced with a new Warmflow condensor boiler.

I know a good plumber who has been doing bits and bobs for me, and he works with Warmflow boilers. I do see a lot of ads for oil Grant boilers but will probably go for what the plumber works with.

No grants at the moment here unfortunately where I live so it will be full price around £2200.

Probably I have been putting off getting a new boiler for a long time, who wants to spend that kind of money, but I think it has to be done now.

Many thanks to everyone for their advice.

Albermarle

As you are getting a new boiler, it is worth giving some thought to changing your hot and cold water system.
Most new systems do not have a cold water tank in the loft, and work directly from the water mains. This is an unvented system. However this would mean replacing the hot water tank with a more expensive type.
Alternatively you could get a combi boiler, where there is no hot water tank at all, as hot water is produced on demand. This will need some pipework changes, so again would be more expensive than just replacing the current boiler.
Worth some thought anyway. 

FreeBear

Albermarle said: As you are getting a new boiler, it is worth giving some thought to changing your hot and cold water system.

Also look at fitting larger radiators so that the system can be run with a lower flow temperature - That will push the boiler further in to condensing mode and give you greater efficiency. If you go 50% oversized, you'll be in a better position to install a heat pump when the time comes.