Heat loss from system overnight.

banjolin

Hello. Not sure how to describe this in technical terms but briefly, I have a 20kw boiler stove (multi-fuel) heating a 300l Joule tank for central heating purposes with a 30 tube solar array for summer hot water. Seems fairly straight forward but it has taken a bit of experience to get the best out of it. The main problem is the amount of heat that seems to be leached out of the tank once the fire goes out at night.

As I understand it, the stove to tank circuit is gravity fed with the thermo-siphoning effect circulating the heat from stove to tank. There is a stat on the pipe from the stove that triggers the pump for the rads once the water reaches the stat temperature. So obviously this draws heat from the tank until such time as the stat trips off sometime after the fire in the stove goes out, usually within about a half-hour.

I assume from that set-up that the circuit from the stove to the tank is unbroken. Therefore, the gravity/siphoning process can continue until such time as some sort of equilibrium is reached and instead of the stove heating the tank the tank is effectively heating the stove. Is that correct? Would this account for the loss of heat from the tank overnight? If it does, can I stop it?

Pete67

If there thermal store is above the boiler stove as it should be, then there would not be reverse circulation - the tank should not be heating the stove. There could be thermal circulation from the store to the solar array at night however or possibly to a heat leak radiator or separate DHW cylinder if you have one but it is difficult to speculate on a cause of the heat loss without seeing the installation.

banjolin

Thanks for that. Its not really a complex system. We have the boiler stove and we have the Firebird solar, both heating the 300 litre tank. The stove is on the ground floor and the tank is above it on the first floor so it seems we are ok there. The tank provides DHW and heats the rads. We have a pump for the radiators with a stat on the hot water pipe from the stove. The only addition we have is that we have to switch on a motorised valve to open the circuit to the rads in the extension. It is so well insulated that we never need to use those rads so we decided to isolate them from those in the old cottage side during the installation.

During the short hot spell we had in May this year the solar was hopping and the tank got quite hot, and somehow the radiators in the cottage started to heat up. I rang the plumber who installed the system and he said turn the stat temperature up and it would not trip the pump to the rads. Apparently the stat on the stove side of the tank (which is located just outside the tank) had tripped and started the pump for the radiators. It was set at 60 degrees. I turned it up to the max, and the rads did not come on again. But it seems certain that if the tank gets hot enough the hot pipe from the stove gets hot enough to trip the stat and turn on the pump. I don't know if the water was moving like it does when the stove is lit or if the heat from the tank is heating the pipe itself (seems unlikely).

Whether any of this is relevant to the apparent heat loss from the tank is beyond me. There is some interplay between the stove circuit and the solar set up, but what it is I can't fathom. Firebird have told me that there should be no leakage of heat from the tank to the tubes if the system is correctly installed. The plumber says it is correctly installed. I'm losing heat somewhere.

Dtp1979

Is the cylinder a pressurised cylinder?
A few pics of the Hotpress would help too

banjolin

I don't actually know if it is pressurised or not. I have attached a few snaps of the installation if that helps to make sense of it. Like I said, I think it is fairly standard set up. If heat loss back to the stove is a non-runner then it must surely be the solar. I just don't know enough about it to work out what might be causing it.

Is it a maintenance/servicing issue? The plumber who installed it is a good plumber but as much use as tits on a bull when it comes to explaining anything. He was the fifth plumber to look at the job and the only one who would quote for it. But I honestly get the feeling that he installed it with a manual and really doesn't fully understand it himself.

Dtp1979

banjolin wrote: »

I don't actually know if it is pressurised or not. I have attached a few snaps of the installation if that helps to make sense of it. Like I said, I think it is fairly standard set up. If heat loss back to the stove is a non-runner then it must surely be the solar. I just don't know enough about it to work out what might be causing it.

Is it a maintenance/servicing issue? The plumber who installed it is a good plumber but as much use as tits on a bull when it comes to explaining anything. He was the fifth plumber to look at the job and the only one who would quote for it. But I honestly get the feeling that he installed it with a manual and really doesn't fully understand it himself.

Could you take better pics? Maybe ones that show the Hotpress as a whole so I can see where pipes are going

Wearb

Not sure but that pipe stat looks to be either fully on or fully off. ?

Sam Kade

Dtp1979 wrote: »

Is the cylinder a pressurised cylinder?
A few pics of the Hotpress would help too

I wonder would it blow up? I remember a few years ago telling you about my boiler stove and you told me it would blow up, still waiting

Wearb

Sam Kade wrote: »

I wonder would it blow up? I remember a few years ago telling you about my boiler stove and you told me it would blow up, still waiting

Ah well it must be ok then :eek:

Dtp1979

Wearb wrote: »

Ah well it must be ok then :eek:

Yes, that's right wearb. Just because it hasn't means all is ok.