Convection starts un the thermal store and the momentum of said convection will cause this.
2 port valve will sort it.
2 port valve will sort it.
Boiler isolation valves
- Thread starter Diwali
- Start date
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I do not know if the pump is running. I suspect it could be. Why else would circulation take place. At that across a horizontal pipe run.
Gravity feed pipe required cylinders that had low number of coil turns in the cylinder ( pumped indirect coils did not support gravity circulation ( been there, have been caught out and had to convert to pumped)), pipe runs were more often in 1” or 28mm pipe and also run was either at all time rising if not vertical.
If the boiler is at a lower level, without pumped primary circulation cannot take place. Are you taking bets that pump is not running and that OP is aware what the pump looks like and SURE the pump he is looking at is the the pump that is the culprit not actual pump that is doing the dirty.
Side note. Two days ago I was disconnecting a fire that was to be removed to make place for a log burner. This fire was installed at some point after the back boiler was removed and a combi fitted elsewhere. Fixitflav, pay attention here……
to left of the fire under the flooring where I was to disconnect the gas pipe, would you believe there is a pump that is wired up but not in use? The pump that is operational is in the boiler. Unused pump use to be operational for the back boiler. To a lay person touching this pump, they would say the pump is not running but the one in the boiler could be heating the rads.
Until all the facts are known, and a site visit is carried out, any speculation will be based on work experience And not idle speculation.
I suppose if it's a nice quiet pump, and an oldish one without any LEDs, it could be running without the OP knowing, but it seems unlikely. If the boiler is higher than the HW cylinder there could be convection, we need the OP to confirm layout. He said there are vertical pipe runs, so it's either above or below!
Interesting, but there's been no indication from the OP that it's a back boiler conversion. If it is, and it's a system boiler, that could be the problem. He only said it's a Worcester boiler, we don't know whether it's heat-only or system. He's said he has no motorised valves. He has a cylinder stat, be good to know how the system is controlled. Adding a 3-port valve and updating the controls (depending on more detailed information) would improve the system, and fix his current problem.
OP - more information needed!
Look at the bottom of the boiler, from the left hand side the 2nd pipe from the left is the flow it has an isolation valve just close it
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Thanks again for all the comments.
Some details of the system:
Boiler: Worcester Greenstar 8000 Life. LPG. (Sealed system) Only heats the cylinder - no other function.
Thermal store: McDonald Thermflow 250l with F & E tank. Vented
Both units are installed on the ground floor with the boiler mounted slightly higher than the boiler flow connection on the cylinder. There are no external valves in the flow and return pipework between the two units. The 22mm pipework runs from the boiler vertically to the first floor where it runs (under the floor) to the point where it runs vertically down to the cylinder. The flow and return run in parallel. The length is approx. 10m
Electrically, there is one supply only to the boiler panel. There are no other electrical feeds to the boiler. When powered on the boiler is controlled by a stat via a Danfoss programmer which takes its power from the boiler panel.
Normally, in winter months the system works and controls well with no issues. It is less than 2 years old.
In summer, to save costs, the boiler is switched off at the local isolator AND at the db (to avoid it being switched on inadvertently). The immersion heater is then used to heat the cylinder for DHW.
Following some of the earlier comments, I’m now of the opinion that convection is the cause of hot water circulating through the boiler. But.... how to stop it?
Are these valid options? :
1. Drain the system - this means refilling at the end of summer and adding inhibiter?
2. Installing isolation valves in the pipework - I believe this is a BIG no-no (and possibly illegal?)
Thanks again.
Some details of the system:
Boiler: Worcester Greenstar 8000 Life. LPG. (Sealed system) Only heats the cylinder - no other function.
Thermal store: McDonald Thermflow 250l with F & E tank. Vented
Both units are installed on the ground floor with the boiler mounted slightly higher than the boiler flow connection on the cylinder. There are no external valves in the flow and return pipework between the two units. The 22mm pipework runs from the boiler vertically to the first floor where it runs (under the floor) to the point where it runs vertically down to the cylinder. The flow and return run in parallel. The length is approx. 10m
Electrically, there is one supply only to the boiler panel. There are no other electrical feeds to the boiler. When powered on the boiler is controlled by a stat via a Danfoss programmer which takes its power from the boiler panel.
Normally, in winter months the system works and controls well with no issues. It is less than 2 years old.
In summer, to save costs, the boiler is switched off at the local isolator AND at the db (to avoid it being switched on inadvertently). The immersion heater is then used to heat the cylinder for DHW.
Following some of the earlier comments, I’m now of the opinion that convection is the cause of hot water circulating through the boiler. But.... how to stop it?
Are these valid options? :
1. Drain the system - this means refilling at the end of summer and adding inhibiter?
2. Installing isolation valves in the pipework - I believe this is a BIG no-no (and possibly illegal?)
Thanks again.
Last edited:
Thanks Jeff, but, excuse my ignorance, how does the 2 port valve work? The boiler provides heat only to the thermal store. DHW and CH source their heat from the thermal store. They are not connected to the boiler.
Why do you think using electric in summer for the HW is cheaper? Have you taken readings to compare with gas? Electric costs about 4 x gas per kWh, and though nearly all the electric power goes into the water, gas has some losses due to boiler efficiency and pipework heat loss, it's unlikely to turn out dearer. But gas has the downside of heat loss in hot weather might make the house too hot.
I think we've established that the problem is due to convection. Convection flow will be out of the thermostore top connection, opposite direction to the pumped flow. A non-return valve, suitably located, could be the answer.
Draining down every year seems a bit of a faff. I don't know about legality of a manual iso valve, perhaps gas safe guys can comment. An alternative could be a motorised valve (as Jeff said), with limit switch to fire the boiler only when the valve is fully open (as on an S-plan system)
It doesnt matter the valves are still where I already told you they were, just close the flow valve 20 second job
To understand the problem, one needs to know what is in place else rest is speculation.
Fixitflav, TWO pumps here as I tried to explain in previous post, both operational only present situation is one is out of action as boiler is not powered . OP perhaps is assuming power OFF at the boiler means no circulation to radiators.
Cylinder is heated by immersion heater but issue with wiring or control ( sticking relay perhaps??) activates the CH PUMP resulting in heat to radiators. No heat is coming from the boiler as it is not powered.
Boiler is a slave to the cylinder, it does not supply heat to the radiators, cylinder does.
Cylinder controls the boiler. A demand to boiler will be ineffective as boiler is OFF
Heat for the radiators comes from the cylinder
It is not uncommon for pump to be fitted with check valves- do not know if that is the case.
Cylinder is on upper level. No convection possible to lower floor, nor to same level as rads will almost certainly not support convection circulation.
Pipe run boiler to cylinder is immaterial in this case.
He hasn't said anything about unwanted heat at the radiators, only the boiler to cylinder pipework.
Agreed
If my theory is correct, a check valve on the boiler pump would stop the (backward) convection, so there isn't one.
He says "Both units are installed on the ground floor with the boiler mounted slightly higher than the boiler flow connection on the cylinder." Though just what the levels are isn't clear.
Convection to the rads isn't the problem.
Not with you. That's the pipe that's getting hot when it shouldn't
Boiler demand to control motorised valve and the end switch to fire the boiler.
Basic but effective.
Suggest you look at the manual for the cylinder.
Thank you all. I’m impressed by your expertise and advice.
To summarise my understanding of the issue based on the comments:
1. The boiler is slightly higher than the thermal store resulting in convection of hot water running in reverse via the boiler flow. This is enough to cause a constant flow of hot water through the boiler.
2. The valves within the boiler panel are slotted but were too tight to turn. Logically, as was suggested, closing the valve would stop the circulating hot water but I don’t have the confidence (nor the experience) to try forcing it.
3. Adding valves (NRV, 2 port v/v etc.) seems to offer the best solution and l will discuss this with the boiler engineer on his next service visit.
However, assumption is the mother of all cock ups as they say and I had assumed electricity (immersion heater) would be cheaper than LPG (the boiler). Someone queried my decision (thanks fixitflav) which made me check the facts:
Guess what? I’m switching back to LPG!
Appreciate all the help. I’ve learnt a lot and will save money in future.
Thanks.
To summarise my understanding of the issue based on the comments:
1. The boiler is slightly higher than the thermal store resulting in convection of hot water running in reverse via the boiler flow. This is enough to cause a constant flow of hot water through the boiler.
2. The valves within the boiler panel are slotted but were too tight to turn. Logically, as was suggested, closing the valve would stop the circulating hot water but I don’t have the confidence (nor the experience) to try forcing it.
3. Adding valves (NRV, 2 port v/v etc.) seems to offer the best solution and l will discuss this with the boiler engineer on his next service visit.
However, assumption is the mother of all cock ups as they say and I had assumed electricity (immersion heater) would be cheaper than LPG (the boiler). Someone queried my decision (thanks fixitflav) which made me check the facts:
Table of heating costs in the average home
- Mains Gas – 4p / kWh
- LPG Gas – 7.5p / kWh
- Heating Oil – 6p / kWh
- Bottled Gas – 14p – 32p / kWh
- Electricity – 15p / kWh
Guess what? I’m switching back to LPG!
Appreciate all the help. I’ve learnt a lot and will save money in future.
Thanks.
Last edited:
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