Fixing & optimising my heating system (oil + log boilers).

Soldato
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When we moved in to this house a few years ago I wasn’t familiar with oil fired or biomass boilers in any way at all. This was the system that greeted us:

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Look at the size of that water tank on the right of the image! 3,000 litres apparently; it’s an accumulator tank, a sort of battery storage of hot water which is critical for the log boiler to operate safely and efficiently as you can't just switch it off like you can with an electric, gas or oil boiler.

Initially we just fed it heating oil and got on with other jobs around the house as you do when you first move in. However, I was shocked at how much heating oil the system consumed, probably around 1,800 litres between November to February. That was due to a few factors – we treated the house like our old place where I’d just replaced the gas boiler which was really efficient and cheap to run and that house was really well insulated. This house was larger, not as well insulated and in a much colder climate than the previous and of course those were the winter months. The other factors of high oil consumption were down to the lack of maintenance and existing faults ignored by the previous owner. Some faults were downright dangerous too.

We used the log boiler often and it was a novelty at first but with having to clean it so often it became quite the chore. The water temperature when running the log boiler was noticeably hotter, through the radiators and domestic hot water, with the latter becoming too hot more often than not. At one point the hot water was more than 80C at the tap. Dangerous and wasteful.

I needed to optimise the system to reduce the oil consumption and tame the log boiler but then covid hit. Getting a knowledgeable and dependable plumber in to check the system was nigh on impossible even after the lockdowns. One plumber did grace us with his presence but didn’t come back! Well, I'm not a plumber but I’m a multidisciplined engineer so I thought it’s time to research and understand the system and just do it myself.

I installed a Hive Thermostat system to replace the ancient Horstmann controller and the inaccurate dial type thermostats. This did improve things due to the greater granularity of settings and much more accurate temperature detection, but more could be done.

First, the understanding the plumbing. I traced each pipe and made a pretty picture:

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Then I traced the wires for each component to determine their purpose. For example, how does the oil boiler know not to come on when the log boiler is running? Pipe thermostat!

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The cable diagram is good for faulting and wiring but for understanding the circuit I simplified it:

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I’ll post more later with what I have done already, the faults I’ve fixed and what I still plan to do. Hope you find it as interesting as I do :) .

Edit: Reduced schematic images sizes.
 
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Very interesting. Any reason why you have a partially open bypass?

Thanks, and I wondered that too. The purpose of the partially open bypass is in event that if one of the motorised valves (no.2, 3 or 4) fails to open and all the others are closed, then water cannot flow anywhere, the pump will keep pumping in to an effectively closed circuit and the boiler will keep heating the water. The oil boiler will trip out because of it's built in over-temperature check but the log boiler won't/can't. Pressure and heat will build up and something will break :eek:. Having it partially open relieves some of that pressure/flow at the cost of some heat being returned to the system.

The bypass valve in my circuit is just a simple gate valve whereas nowadays the recommendation is to fit an automatic bypass valve which only opens at a set pressure. Much more efficient and safe. I was going to fit one to replace the manual one but the pumps I've bought (Grundfos UPS3) state not to use an auto-bypass valve if using proportional pressure mode.
 
Thanks, and I wondered that too. The purpose of the partially open bypass is in event that if one of the motorised valves (no.2, 3 or 4) fails to open and all the others are closed, then water cannot flow anywhere, the pump will keep pumping in to an effectively closed circuit and the boiler will keep heating the water. The oil boiler will trip out because of it's built in over-temperature check but the log boiler won't/can't. Pressure and heat will build up and something will break :eek:. Having it partially open relieves some of that pressure/flow at the cost of some heat being returned to the system.

The bypass valve in my circuit is just a simple gate valve whereas nowadays the recommendation is to fit an automatic bypass valve which only opens at a set pressure. Much more efficient and safe. I was going to fit one to replace the manual one but the pumps I've bought (Grundfos UPS3) state not to use an auto-bypass valve if using proportional pressure mode.

I was going to say, definitely change that for something that makes a decision instead of being partially open all the time. Waste of energy.

With regards to the pump then, I wonder if there’s a better way of doing it so that you don’t have a bypass. Annoyingly, I don’t have the answer. When I’m not off work I can ask around as someone at my place may know the answer.
 
I was going to say, definitely change that for something that makes a decision instead of being partially open all the time. Waste of energy.

With regards to the pump then, I wonder if there’s a better way of doing it so that you don’t have a bypass. Annoyingly, I don’t have the answer. When I’m not off work I can ask around as someone at my place may know the answer.

I agree, it is a waste of energy. Some of it is conserved through the system by means of the Thermomatic K constant heat regulator, which blends the return water with the supply. However it's target temperature has been set to 80C so it won't blend if it's logic determines not to. If no blending is required then the return water will be sent to the bottom of accumulator tank where it'll mix (not really mix per se, thermodynamics comes in to play here with "heat layering" or "layered or stratified charge storage", science huh!) with cooler water at the bottom of the tank. That cooler water returns to the boiler to be heated again. There is a waste of energy if it's not being put to use.

I digress!

Although I've determined that proportional pressure suits my system more, I could change that. Some trialling and testing is required for which mode operates the best. I already have the pumps, just not fitted them yet hence why I've not touched the bypass valve. Here's what the blurb for the Grundfos USP3 pump states:

Proportional pressure
We recommend proportional-pressure mode in variable flow systems with relatively large pressure losses in the distribution pipes such as:
• two-pipe heating systems with thermostatic valves and long distribution pipes
• two-pipe heating systems with thermostatic valves and high pressure losses in system parts with total flow
• primary circuit pumps in systems with large pressure losses in the primary circuit.
Note: Proportional-pressure mode is not recommended in heating systems that includes an automatic bypass valve to ensure a minimum flow for the heating appliances.

Constant pressure
We recommend constant-pressure mode in variable flow systems with relatively small pressure losses in the distribution pipes such as:
• two-pipe heating systems with thermostatic valves and dimensioned for natural circulation (former gravity systems)
• two-pipe heating systems with thermostatic valves and low pressure losses in system parts with total flow
• one-pipe heating systems with thermostatic valves or pipe balancing valves
• underfloor heating systems with zone valves
• primary circuit pumps in systems with small pressure losses in the primary circuit.

Constant curve
We recommend constant-curve mode in constant-flow systems, where both a constant flow rate and a constant head are required, such as:
• heat surfaces
• replacement for uncontrolled circulator pumps, for instance integrated in boilers.

It would be great if you could ask someone at your work, the more info the better :).
 
In Hot Water.

The first major fault that I fixed on the heating system was incredibly hot water, but only sometimes. That might sound funny, but the hot water was almost 80C, more than enough to seriously burn if you put your hand under a running tap. You could run a bath pretty quick though! The hot water should be in the range of 55C - 65C depending on what the setting of the boiler and the DHW tank's thermostat and some people do set lower than this. Worthy of note - this fault only occurred when the log boiler was being used, not the oil boiler. The thermal cut-out on the DHW tank would have course be tripped requiring a manual reset, but this was only an issue when using the oil boiler and requesting hot water only and with no zone heating. The boiler wouldn't get the fire signal through the tripped thermal cut-out. Only the oil boiler has an electrical circuit, the log boiler has no electrical connection. This is something I don't like and I'll be looking to integrate something in the future.

Anyway, long story cut a little bit shorter, the problem was a faulty (or fudged) zone valve actuator for the DHW plumbing circuit (Motorised Valve 4 in the schematic). This how the old one looked mounted on it's valve body.

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Doesn't look right at all, it should be inline with the pipework, not at an angle so I put it back on straight. It fell off :rolleyes:. On inspection the valve body itself was in the open position and would open and closed perfectly fine by hand but the motorised actuator itself wouldn't mate with the shaft/spindle of the valve, the actuator was too worn. So when the actuator tried to open or close the valve it had no effect.

That explained the reason for both the really hot water and the high oil consumption. The schematic below illustrates it better in words, but here goes. Whenever heating for either zone 1 or 2 or both was called the DHW would leech the hot water meant for the radiators because it's circuit was always open. As in the schematic below with zone 1 active the radiators would still get heated as the water circulates around the system constantly getting heated by the log boiler. The duration of how long this would occur depended on the room thermostat for the zones (to run Pump 2) and not the hot water cylinder thermostat. When the pump isn't running the accumulator tank would store the heat instead.

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So why would this only happen with the log boiler and not the oil boiler? That is because the oil boiler has it's own temperature set-point and thermal cut-out and would detect when the water was hot enough and stop heating. Plus the fact that the log boiler just gets the water hotter, quicker and constantly heats as long as it has fuel to burn. Only a lack of air or fuel stops the log burner.

Replaced the motorised actuator and it fixed the problem of over-heating the hot water and also reduced the oil consumption :).

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However, this immediately introduced another problem - severe water hammer :mad:.

Edit: Reduced schematic image size.
 
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Stop, Hammer Time!

Time for the next instalment of my enthralling central heating adventures I'm sure you'll agree :D.

As I left off in my last post as soon as I replaced the zone valve actuator for the domestic hot water circuit this introduced water hammer. In case you don't know what water hammer is, it is "the result of a pressure surge, or high-pressure shockwave that propagates through a piping system when a fluid in motion is forced to change direction or stop abruptly". More info here (https://www.dft-valves.com/applications/water-hammer)

In my system the noise and banging was so loud it could be heard and sometimes felt all around the house at the exact time the hot water heating was turned off by the Hive. It only ocurred when this particular zone valve closed and oddly none of the other zone valves. I now believe that the faulty zone valve was left physically disconnected on purpose by the previous owner as a means of stopping the water hammer :rolleyes:. It probably caused the damage to the actuator in the first place. After replacing the actuator and foolishly living with the water hammer effect it wasn't long before it would claim it's next two casualties, the valve actuator for Zone 1 and also Pump 2.

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The toothed cogs of the actuator were chewed up so it was skipping when trying to open/close and the motor of the pump no longer turned. The former probably caused the latter to fail...

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Being in a bit of a pinch at the time I replaced the original Grundfos UPS 15-60 pump with a cheaper equivalent BritTherm pump which I would not recommend.

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It's very whiny and at a particularly annoying frequency that seems to resonate and travel along the pipework. Also when bleeding the air from it it seems to capture water behind it's rating plate and just dribbles for ages. This and the other pump will be replaced with Grundfos UPS3 pumps soon.

The water hammering had to be fixed as a matter of urgency before something else broke or even worse, burst a pipe or connection. The thought of hot water at 80C skooshing out at 2bar was enough. A decent plumber was still as hard to find as diamond encrusted unicorn poo and probably just as expensive. A bit of research led me to considering installing an anti-water hammer device between the DHWW motorised valve 4 and Pump 2 to absorb the hydraulic shock but that felt like a countermeasure to an existing fault. I found it hard to believe that the system was designed with such a flaw, something else had to be faulty.

Back to the drawing board as it were, with the "shock path" plotted out it was clear what was to be checked next - the expansion vessel for the heating.

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I set about checking the pressure of the heating's expansion vessel and repressurising it if necessary, it has a schrader valve at the top for this purpose. Before draining the system (which is required for testing and repressurising the vessel) I gave the schrader valve a little press as by now I was sure what was going to happen. Sure enough, water trickled out. It should be air! The membrane of the expansion vessel had obviously failed.

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It wouldn't stop trickling out. As the system was still under pressure (2bar) the water could overcome the spring of the schrader valve just enough for it to leak out. The system had to be drained and a new expansion vessel fitted.

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After testing that the new expansion vessel was still at 1.5bar as from the factory, it was fitted (using Loctite 55 sealing cord instead of PTFE tape) then the system filled and up to pressure to test for leaks. None :).

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Did replacing the expansion vessel fix the water hammer problem? Yes!

A few points to take away from this. Firstly, an experienced plumber would probably have identified the problem almost immediately; a good dependable plumber is worth their salt if you can find one. Secondly, why didn't the previous owner of this house sort this out rather than fudge the DHW zone actuator? I hate to think of the all the wasted energy and money in oil and wood over the past few years, not forgetting replacing the damaged components too.

While the system was drained I installed a magnetic filter, more on that later.
 
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I like it.

That pump is very high in the system, it will burn out if it keeps getting air trapped in it. I would put an automatic bleed valve next to that or even better, drop it down to avoid air trapping in it.
The Grundfos UPS3 is a fantastic pump. The automatic speed pumps from Grunfos are amazing, they save a surprising amount of energy.
 
This is very exciting. I love it when stuff is fixed.

Me too!

I like it.

That pump is very high in the system, it will burn out if it keeps getting air trapped in it. I would put an automatic bleed valve next to that or even better, drop it down to avoid air trapping in it.
The Grundfos UPS3 is a fantastic pump. The automatic speed pumps from Grunfos are amazing, they save a surprising amount of energy.

Thanks, Pump 2 is positioned quite high but it's not the highest point of the immediate circuit, the accumulator tank has an auto-bleed at top of it. This was extremely useful when it came to refilling the system. I hear what you say though (the BritTherm pump was a pain to bleed) and it was another reason to go for the UPS3 pumps as they are auto-bleeding :). I have the pumps already but waiting for when I have enough time and when the system is cool enough to work on. That's not so much lately as the weather gets colder.

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When I fitted the BritTherm pump I also had to change the gate valves as one was welded to the old pump (see a few images up) and the other a bit gritty and worn. I'm expecting the same when I change Pump 1 so the system will have to be drained again just in case. It's why I haven't added any additive to the system yet.
 
With all the recent talk about balancing radiators and such I thought I get the thermal camera out do a bit of checking.

This is the kind of thing I need to put right:

This is the lockshield end of the radiator:

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This is the TRV end of the radaitor:

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I don't know why plumbers do this? Do they forget what pipe is what when they install the radiators?! I've found 3 radiators just upstairs that needs correcting.

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what's the strategy for the accumulator temperature modulation ? needs to be hot enough to provide the hot water, but heating it unnecessarily if the central heating isn't needed would waste energy(accumulator losses.)

will the pump provide you with data to justify/optimize proportional/constant setting - & avoid stressing it.
is the bypass actually automatic or it is just opened when upstairs/downstairs heating valves are both closed , for maintenance.
 
Looks like heat is coming from the lockshield i.e. the return side and not the flow side.

Ah! In reality, it shouldn't make a difference. It might even be better in the respect that the thermostatic head on the TRV won't be affected by the temperature of the TRV itself.

Interestingly as well, in Denmark they always put the thermostatic head horizontally so it's away from the radiator. They also put them top/bottom for better heat distribution (not sure which goes where).
 
Ah! In reality, it shouldn't make a difference. It might even be better in the respect that the thermostatic head on the TRV won't be affected by the temperature of the TRV itself.

Interestingly as well, in Denmark they always put the thermostatic head horizontally so it's away from the radiator. They also put them top/bottom for better heat distribution (not sure which goes where).
Possibly means the radiator is slow to heat up if it has a baffle on the return side.
 
A few questions there,

what's the strategy for the accumulator temperature modulation ? needs to be hot enough to provide the hot water, but heating it unnecessarily if the central heating isn't needed would waste energy(accumulator losses.)

I'm not sure I know what you mean. At the moment I'll be leaving as it is as it really only comes in to play when the log boiler is running, as you can't turn it off immediately like you can with a normal boiler so the heat generated has to go somewhere (when all zones are closed). I agree there are definitely losses with the accumulator like with any storage, especially as it's in a garage with a temperature of 5C at the moment. There are some exposed metal blanking plugs that really should be insulated.
I was thinking about some sort of bypass for when the oil boiler is running so it's heated water doesn't go through the accumulator but there are a few issues with that so will likely not bother.

will the pump provide you with data to justify/optimize proportional/constant setting - & avoid stressing it.

Not sure about the pump yet as I've not had the opportunity to fit them. I have been thinking about what metric to use to decide on the best setting but there are so many variables. I will try the various type and compare performance and behaviour, see if anything is actually different. I need to know the impact of the pump settings with dynamic radiator valves since I've decided to use them in the future.

is the bypass actually automatic or it is just opened when upstairs/downstairs heating valves are both closed , for maintenance.

The bypass valve is a purely manual gate valve and is currently open 20% all the time. Pretty inefficient. However, the heated water is recirculated and depending on it's temperature it's either blended with the incoming hotter water (using the Thermomatic K constant heat regulator) to reduce the amount from the boiler or it's directed to the accumulator tank and back to the boiler.
I was looking at fitting an automatic bypass valve as I've mentioned before but that will depend on the UPS3 pump setting I use. I could close it completely but that creates quite the risk should any motorised valve fail to open when the pump(s) are running.
 
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