No hot water cylinder thermostat

Pigus

My mum has lived in the same cottage for 40 years and has a very basic combined water/heating system with oil boiler, cylinder and immersion. No separate hot water/heating timer control, manual room thermostat.

We have enquired with the people who recently serviced her boiler if a dual heating/water control could be installed. They have said that they would need to plumb in a valve to allow that to work - no prob. But they also said that the cylinder has not water thermostat and this would need to be installed. So far so good.

However, my mother told me recently that the water has got too hot to touch. In 40 years I had never noticed this. I visited and she was right - radiators nice and hot but tap water too hot. I wondered whether, during the boiler service, the boiler temp had been left too hot. So I ran the water to cold and lowered the boiler temp. Unfortunately, this did not solve it.

I called the heating company and they explained that this is because the cylinder has not thermostat. I queried this because surely, I suggested, the cylinder water temp can not get hotter than the water coming from the boiler and running through the heating coil. Heat exchange can only happen if one body of water is cooler than the other, no?

But they told me this is not the case. They said that without a cylinder thermostat the boiler water would continue to heat the cylinder water, so long as there is a lower rate of heat loss through water usage.

Is this true? My basic physics tells me not. Surely, ultimately, there would be no heat exchange and the boiler thermostat would react accordingly, i.e. the return flow from the house would remain hot and no boiler heating would be required. Which makes me question, actually, whether it is the boiler's thermostat which is not working correctly - even though a cylinder thermostat would be a good idea.

psb75

Please provide some pictures of your system and you will get the best response from folks on this forum.
Pictures reveal much.

Pigus

Hi, thanks for the suggestion. Appreciate pics would help but I have none and my mother lives 2 hrs away.

psb75

Understood. So, you'll have to be really (esp.) precise with your terminology and descriptions as the questions come in. Here's mine: do you have an indirect domestic hot water tank that is heated by the boiler sending boiler water through a coil in the bottom of the water tank? And I believe you are saying that the tank does not have an aquastat (temperature sensing device) that communicates with the boiler. True?

Jamie Hall

Well, without pictures this may take some time -- particularly since clearly some terms we commonly use and the terms you are using aren't really quite the same.

But let's see here.

Would it be correct to say that your mum's place is heated by an oil fired heater, and that somewhere in the system there is a pump which circulates water from that heater through radiators and back to the boiler? Now there are several possibilities, if that is so, and we really need to know which one is correct. Does the room thermostat start the boiler, and then, after a period of time, the pump comes on? Or does the room thermostat start the pump, and then, after a period of time, the boiler comes on? Or do both the boiler and the pump come on at the same time?

Now the hot water cylinder. Would it be correct to say that this is a water storage tank? You mention immersion to heat it. Would it be correct to say that by that there is a pipe from the boiler, perhaps with another pump, to the tank, and then coils in the tank, and then a pipe returning to the boiler? Or are the pipes to this tank directly from the heating pipes, and water circulates through them whenever the heating circulation is happening?

That's kind of for starters.

While you are working on those, however, the hot water system -- however it is controlled -- should, for safety, have a thermostatic mixing valve on it. These valves take water from the cold water line and from the output from the hot water tank or cylinder, and mix it to control the output temperature to the user. These are common (indeed, required) in many jurisdictions in the United States and Canada, but I am not sure where you are located so they may be less common where you are. Common or no, they should be available, and a competent plumber should be able to install one without much trouble. I very strongly recommend that you have that done, and have the output set to no more than 105 F or 40 C for your mum's safety.

Pigus

psb75 said:

Understood. So, you'll have to be really (esp.) precise with your terminology and descriptions as the questions come in. Here's mine: do you have an indirect domestic hot water tank that is heated by the boiler sending boiler water through a coil in the bottom of the water tank? And I believe you are saying that the tank does not have an aquastat (temperature sensing device) that communicates with the boiler. True?

Yes on all Qs

Pigus

Yes, indirect domestic tank system, no aquastat

Pigus

"Would it be correct to say that your mum's place is heated by an oil fired heater, and that somewhere in the system there is a pump which circulates water from that heater through radiators and back to the boiler?"

YES, pretty sure.

"Now there are several possibilities, if that is so, and we really need to know which one is correct. Does the room thermostat start the boiler, and then, after a period of time, the pump comes on? Or does the room thermostat start the pump, and then, after a period of time, the boiler comes on? Or do both the boiler and the pump come on at the same time?"

I CAN NOT BE SURE unfortunately. My memory is that the room thermostat triggers the water pump for sure. Whether it triggers the oil boiler at same time I really don't know.

"Now the hot water cylinder. Would it be correct to say that this is a water storage tank?"

YES

"You mention immersion to heat it."

This an alternative, element heater, for quickly heating the water when the tank has run cold. However, I think she uses it also in summer when there is no need for the heating system to be on - so heating and hot water are not decoupled in her system.

"Would it be correct to say that by that there is a pipe from the boiler, perhaps with another pump, to the tank, and then coils in the tank, and then a pipe returning to the boiler? Or are the pipes to this tank directly from the heating pipes, and water circulates through them whenever the heating circulation is happening?"

I can not be sure of the exact piping arrangements, sorry.

"While you are working on those, however, the hot water system -- however it is controlled -- should, for safety, have a thermostatic mixing valve on it. These valves take water from the cold water line and from the output from the hot water tank or cylinder, and mix it to control the output temperature to the user. These are common (indeed, required) in many jurisdictions in the United States and Canada, but I am not sure where you are located so they may be less common where you are. Common or no, they should be available, and a competent plumber should be able to install one without much trouble. I very strongly recommend that you have that done, and have the output set to no more than 105 F or 40 C for your mum's safety."

Thanks. We're in the UK. That water temp mgnt system was not fitted for older systems here and some are still really old! My mum has lived there > 40 yrs. It's a 400 yr old cottage

Appreciate your time to help, tough I suspect we'll have to get an engineer out from what you say.

Jamie Hall

I kind of figured you were in the UK. That's not a problem! I think that the tempering valves -- water temperature management valves -- are readily available, though if memory serves you will have to get a licensed person to install one (here in the US, for better or worse, the homeowner can do it himself or herself). I really do think it would be a good idea.

psb75

Wow a 400 y.o. cottage! Here in the U.S. that would have to be in Jamestown, VA or Plimouth, MA! But I don't think that even they have bldgs. that old any more.

Jamie Hall

psb75 said:

Wow a 400 y.o. cottage! Here in the U.S. that would have to be in Jamestown, VA or Plimouth, MA! But I don't think that even they have bldgs. that old any more.

They're all over the place in the UK, @psb75 (not so much in mainland Europe -- something about World War II and allied bombing, I think). The building my daughter lived in the first year she lived in Scotland was built in 1584, as I recall, and places I have lived in on Orkney have been that old. Very comfortable, though sometimes it takes a little getting used to. That said, bringing them up to anything even close to modern standard is a nightmare.

psb75

True that Jamie. Don't forget...the UK took its share of Axis, air-lifted munitions. Mostly urban though--London, Coventry etc.
I have friends in Northumberland with a 15th c. stone, farm house. It was built as a fortified residence or, "bastle house' to protect from Scottish border 'reivers' i.e. bandits. It is heated with a mod/con boiler and panel radiators. Cozy. Check the weather in northern UK today! Storm w/ snow and +80 mi./hr. winds.

JakeCK

psb75 said:

Wow a 400 y.o. cottage! Here in the U.S. that would have to be in Jamestown, VA or Plimouth, MA! But I don't think that even they have bldgs. that old any more.

There is a spanish church that is about 400 years old in the southwest, and several native pueblo villages that are much older than 400 years.

Jamie Hall

Come now, @psb75 . Some of my revered ancestors were reivers, from north of Carlisle. Fine upstanding people with an unconventional way of life. The English took exception to their profession and exported them to the Colonies, as they were called, where they settled in the mountains of Virginia, West Virginia, and Kentucky. Some are still there...

And your weather for the last few days really has been pretty horrible (I still have relatives in Orkney, so I check). City folk have no idea -- but those high moors can be really genuinely dangerous in such weather.

Many of those old stone farm houses can be very comfortable indeed, and with remarkably little work -- mostly making sure that the draughts don't get in.

Pigus

Well thanks guys for the history and WW2 lessons Yes there certainly are some very old places here - and across the continent by the way. Allied bombing, like German bombing, focused on cities and industrial centres. Rural areas, provinces were barely touched, and certainly not most of France. Having said that, the Battle of Britain saw a lot of damage across Kent where my dad lived, while the Luftwaffe were fighting overhead and trying to destroy the airfields in summer 1940. He used to watch the dog fights overhead from the school grounds. He said German planes would sometimes offload their ammo anywhere on the way home. He recalls once diving into a shop doorway as a plane screamed down the village high street firing off what was left. One came down in the school grounds too. He had quite an adventurous 5 years, aged 9-14. I suspect that there are still some places where the plumbing hasn't been updated since!

Jamie Hall

Now having gotten the history lessons out of the way (my relatives places in Orkney had almost no damage -- despite (or maybe because?) one could see the main fleet anchorage in Scapa Flow from there!). But so right -- some of the cities took an awful beating, on both sides. As one US general once said, "war is hell".

Where were we on your heating? Oh yes. tempering valves. I really do think you should have one installed for your mum, and then not worry much about the rest of the operation. Can you do that?

Pigus

Yes I think we will ask a heating engineer to pick up your recommendation and sounds like that should fix it. Thanks all for your help and advice.