overheating problem with Warmflow oil fired boiler.

Discussion in 'Plumbers' Talk' started by Martin 1, Nov 7, 2019.

  1. Martin 1

    Martin 1 New Member


    I have an oil fired heating system, approx 17 years old.
    Its a Warmflow boiler with a Riello oil burner. The unit feeds the radiators plus a Santon pressurised storage water tank.

    I have 2 issues.
    Occasionally the high level trip activates meaning I have to reset the button.
    I have adjusted the dial to about 2 o'clock, then 3 o'clock and 4 o'clock. The boiler obviously cuts out when the thermostat temp is reached, but at these lower settings it seems the boiler is cycling on and off well before the desired house temp is reached. Surely the boiler should stay on until the temperature I set in the house thermostat is reached and then cycle on and off to maintain that heat?
    I understand the boiler thermostat is there to prevent the boiler overheating, but why is it cycling on and off way before the house temp is reached, and on occasion, tripping off completely needing a reset? In other words, I suppose, why is it overheating?

    Recently, I have had replaced the red expansion tank, had a new Wilo Sonos Pico pump fitted and had a Fernox TF1 filter fitted.
    The system was drained down a few weeks ago, cleaner added, run for a few days then drained again, and then inhibitor added and refilled..

    None of the radiators are cool, and all heat to very hot when allowed too, they also bled correctly and there is no sound of air in the system so I don't think there are any issues there.

    The expansion tank shows just under 1bar when cold, and about 2 bar when hot.
    Ive checked every valve etc and everything is functioning externally as it should, yet my boiler still seems to be overheating?

    Can anyone advise what might be causing the boiler overheat?

    Read more: https://www.diynot.com/diy/threads/oil-burner-not-functioning-properly.532867/#ixzz64ccLdNPn
  2. Heat

    Heat Screwfix Select

    Boiler Thermostat could be faulty.
    If water in system pipes seems to reach very hot temperatures when stat is near minimum setting, then stat is definitely faulty.
    Boiler will cycle on and off as it heats the system, but obviously will cycle worse if flow is poor and not enough to cope with boiler power output. Wrong pump, or faulty pump or pipe blockage would also do that.
    Also pipes from boiler badly installed buried in ground would lose heat quickly causing cycling.
  3. kiaora

    kiaora Screwfix Select

    Boiler over heat, ?
    From your description, it seems you may be asking the wrong question.
    The boiler stat turns off the boiler when the water in the water jacket is hot.

    it seems the problem is the flow rate through the boiler and/or system pipe work.
    Is there a bypass near the boiler ?

    this can be a radiator close to the boiler acting as a bypass, and it need throttling back ?
    You may have air in the flow or return pipes, this can fool you,
    You can bleed the rads as much as you like, and it still can air locked

    good luck
  4. Heat

    Heat Screwfix Select

    [ Occasionally the high level trip activates meaning I have to reset the button. ]

    If the thermostat reset on high limit trip is having to be reset, then control stat is likely faulty, or control stat is turned very high and heat not getting away
  5. Martin 1

    Martin 1 New Member

    The boiler thermostat is brand new, I just changed it a few days ago as I suspected the old one might be faulty, but the problem persists. I have nest stats in the house, and at the moment, I cannot get the temperature in the room the stat is in above 19 deg. The boiler is not tripping at the minute, but the boiler thermostat is switching the boiler on and off meaning its not getting a good run to bring the house temp up further. I honestly don't think flow is the issue either. The system was drained down, cleaner added, run for a few days, drained and flushed again with fresh water, then filled and inhibitor added. All rads bled fine and are hot to touch with no cold spots.

    Kiaora, the boiler stat is the one pictured below. The only thing really that has changed recently apart from the new Wilo pump is the draining and flushing of the system. There doesn't seem to be any air, but how could I check further after bleeding the rads which I done successfully? Also the system is silent and only water coming out of the bleed vents on the rads.
    Also, I have. Fernox TF1 filter fitted. When I 'run' it to flush the magnite out of it its a really powerful flow so I am unsure if there is a flow issue.

    Attached Files:

  6. Martin 1

    Martin 1 New Member

    Where would the control stat be located? I am only aware of the boiler stat fitted onto the oil boiler itself (as in the picture in my last post), this has the high level trip reset built in to it, and the nest stats in the house. Is the control stat something else?

    I have tried the boiler stat at 2,3, 4 5 and full, but eventually the boiler clicks off no matter how low or how high the dial is set at.
  7. Heat

    Heat Screwfix Select

    Sorry I confused you. The control stat is the main stat part of the stat you have replaced. The reset is just the second part of it that limits the heat (cuts off) if control stat fails
  8. Martin 1

    Martin 1 New Member

    oh I see. I'm really stumped by this. As I say, flow seems fine and I don't hear or suspect air in the system, pump, boiler stat, expansion tank all new.
    I cleaned out the inside of the boiler and cleaned the baffles, replacing them as per manual (weren't overly dirty anyway).
    I wonder would another drain and fill help. I have a TF1 filter on, and there isn't a huge amount of gunge attracted to the magnet at the moment. Ive cleared it about 4 times over the lat few weeks to check, so Im not sure how beneficial another drain and refill would be.
  9. Heat

    Heat Screwfix Select

    Keep that thermostat turned down to help avoid the high limit cutting out in meantime.
    I dislike that stat and find they overheat
  10. Martin 1

    Martin 1 New Member

    It was the direct replacement for the warmflow boiler. Yes, Im trying to keep the stat at 3-4. Not solving the issue though. It should run at 3-4 without stopping and starting every 10 minutes. Any other advice greatly appreciated.
  11. Heat

    Heat Screwfix Select

    I know it is not an answer to your problem, but I would advise you turn the stat to 1 or 2 max.
    I work on oil and notice those stats overheat. Had to replace a lot.
    Terrible stat compared with the older Warmflow Imit stats.

    Your circulating pump could be faulty, or impeller has gunge in it, or pump is closing down in power.
  12. Martin 1

    Martin 1 New Member

    The pumps new as well :( I replaced all of these things to try and improve the situation. I will remove the impeller and have a look to see if any thing stuck there.
  13. Martin 1

    Martin 1 New Member

    Went out to the garage and unscrewed the pump head. Impeller is spotless, like new. Also the water is clean. Ran the impeller and there are no issues. Its a pico with a digital display, it says its running at 40w.

    Im reluctant to get another stat just a week after this stat was bought, but do you think it would make a difference? Which stat would fit, its a Warmflow 70/90 boiler.
  14. Martin 1

    Martin 1 New Member

  15. TheMorg

    TheMorg Active Member

    Have you checked both pump valves are fully open?
  16. Martin 1

    Martin 1 New Member

    Both valves open. Ive bought a new IMIT stat to try today.
  17. Martin 1

    Martin 1 New Member

    Right. Init boiler thermostat fitted and getting exactly the same results, boiler cycling on and off long before desired temp in the house is reached. (I left the Init stat in the lower mid position, about 65-70 deg. So I have tried a new Init stat, the new warmflow WM2 stat, and of course the original stat (which was obviously ok as well) 3 stat, and all registering that the boiler is overheating.
    I spoke to a heating engineer who was queuing in the plumbing suppliers today while I was in getting the Imit stat. He reckoned it sounded like a flow issue, and if not the pump causing the problem, then potentially air in the system . As he said "preventing heat escaping from the boiler??" Its a new Wilo pump, so I am going to try the old pump again (it was working), and a drain and refill of the system. Anything else I can try? I am trying everything possible before calling a heating engineer, just to rule out what I can first.
  18. Martin 1

    Martin 1 New Member

    So.... Cant try the old pump again as the gate valves I took off with it are virtually welded to the pump and the pump plus welded on ball valves is shorter than the new pump and ball valves.
    I had tried balancing my rads with the closer rads to the boiler having their lock shield valves turned down to minimum, and opened slightly more the further away the rads were from the boiler. I was thinking this might be restricting flow, so I opened all the return valves more, but still the boiler is overheating causing cycling on and off every 5 - 10 mins.
    I took off the pump head and opened each ball valve either side of it, and water gushes out under pressure. Same on the return feed where the Fernox TF1 filter is. Closed the valves either side of the filter, opened the filter drain and opened the ball valves either side in turn, plenty of gushing water under pressure.
    Im really at a loss now. I am going to drain the system tomorrow and refill to see if its an airlock somewhere causing flow issues, but after that I cant think of anything else?

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