Indirect heating to thermal store

Discussion in 'Plumbers' Talk' started by ANDREW HUNTLEY, Dec 4, 2020.

  1. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Hi all. Some advice would be grateful.
    I have a Telford thermal store, 300l capacity which has a heating coil from the baxi 28se system boiler. It takes over 4hrs to heat the store from the boiler. My log burner which is also linked to the store in separate ports takes 1.5hrs to heat the store to 70 degrees.
    The boiler heats up to 90 degrees and the gas turns off until the temp on the boiler reduces before the gas re ignites, the pump is still pumping to the coil
    Speaking to Telford tech man, the boiler should heat the store via the coil within an hour. The system is 7yrs old with no indications of leaks in the coil which also has an auto air release valve. Any suggestions as to why the slow heat up of the store via the boiler.

    Thanks in advance
     
  2. Mike83

    Mike83 Screwfix Select

    Is there any restrictions on the coils pipework from the heating system?
    You’ll have the zone valve on the flow but is it maybe restricted by means of a gate valve on the return.
    What location are the 2 coils on the tank? Are both coils at the same height or is one above the other?
    What temperature is the cylinder stat at?
     
    Last edited: Dec 5, 2020
  3. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Hi thanks for your response.
    I'll answer in same order as questions.
    1. No restrictions from the boiler to coil or return.
    2. Only 1 zone valve on the entire system. (Coil heat or loft rads only)Primary is set to the tank which is in the correct position.
    3. Please see the attached photo for the coil positions. Input is just below mid rank, return is just above immersion coil.
    4 tank stat is set to 70degrees.
     

    Attached Files:

  4. Mike83

    Mike83 Screwfix Select

    When you say it takes 4 hours to heat what do you mean by this.
    Is it that it takes 4 hours for the stat to be satisfied thus turning the zone valve off.
    Or.
    Does it actually take 4 hours to heat the store.
    Is there a chance the store is up to temperature but the cylinder stat isn’t yet satisfied.
    Is that stat in the correct location for the coil.
    If boilers coil is half way up the tank it will never heat the full tank. The stat needs to be above the bottom of the coil to sense any stored heat otherwise the boiler will continue to cycle.
    Finally during this heating up cycle is the flow and return hot?
     
  5. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Hi Mike.
    The zone stat changes from heating the coil to heating the loft rads directly from the boiler pressured.
    The store stat is located 3 inches below the top of coil as per the photo.
    The flow from the boiler is piping hot as well as the return.
    If the water in the store is heating for one hour per morning on the programme, there is only enough hot water for one 10 min shower..I get the second shower!!!. To get the store to around 70degrees for showers and rad heating its min of 4hrs before the store stat is satisfied. The boiler is also set to 70degrees but keeps cycling until the temp drops below 80-90 degrees
     

    Attached Files:

  6. Mike83

    Mike83 Screwfix Select

    How is the thermal store topped up with water?
    Is there enough in it.
    Is the magna valves fully open.
    What does that gate valve do.
     
  7. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Hi Mike
    Store is topped up from fe tank just above store acting also as hot expansion.
    The magna clean us on the rad circuit with valves fully open so not linked to the coils.
    The grey valve is for either the coil heating or loft rads heating which is in primary position for coil heat.
    There is a brass ARV on the coil to release any air in the coil
     
  8. Mike83

    Mike83 Screwfix Select

    Could the coil be scaled up.
    If the flow and returns are hot then there could be limited heat transfer from the coil to the stored water.
     
  9. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    It was drained last year after the boiler ARV was leaking and replaced. The same ARV was replaced a month ago again with a tump of inhibitor into the coil..I would assume the coil should be clean after that?
     
  10. Mike83

    Mike83 Screwfix Select

    I’m talking about the external coil surace.
    There could be a build up on that which will slow down the heat transfer.
     
  11. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Hi Mike
    Yes. I put in 5 sentinel x100 containers into the system 2yrs ago. I would of thought the system should be clean.
    I suppose I could drain a little off and put a few containers of sludge breakup?
     
  12. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Just checked the magnaclean. Spotless water was a wee bit ginger, like a cheap whisky!
     
  13. Mike83

    Mike83 Screwfix Select

    I’m not talking about the insides of the coil.
    I’m talking about the external surface of the coil.
    This will sit inside the thermal store so could be scaled up especially if the store is venting and drawing in fresh water.
     
  14. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Yep. I did put in the store 4 of x100 inhibitor (outside the coil). The F&E tank float is set low so i don't get fresh water into the store volume when the hot water expands and goes down the overflow waste which was happening 4yrs ago.
    The instalers came back and set the ballcock low so I would have only a couple of inches of water in the F&E tank, allowing at least 12inches for water expansion
     
  15. Mike83

    Mike83 Screwfix Select

    It’s certainly strange.
    Everything seems to be covered.
    If the flow in to the coil is hot and the return is also hot that would usually indicate zero issues.
    If there was a problem with the return you would expect the coil connections to cool down as it would lose its heat to the thermal side.
    Is that gate valve at the bottom not just for the hot water return?
     
  16. ANDREW HUNTLEY

    ANDREW HUNTLEY New Member

    Hi Mike. Gate valve is just for the coil heat or loft rads
    The initial system i had was a sealed ss store.
    We decided to have the log burner with wraparound back boiler afterwards.
    So Deco Heat took out the sealed ss tank and retrofitted the copper store.
    The log burner heats up the store within 60-90 mins!!!
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice