Vented central heating system

[Jitzer]

Hello.

We moved into our house in April last year and didn't notice any problems with the heating - the weather being warm enough only to need slight heating occasionally. Come the winter and we have had major problems. We have a Glow worm ultimate 60FF vented system with 10 radiators - 5 up 5 down. We are only able to get the downstairs radiators warm with all upstairs shut off. The alternative is we have hot radiators upstairs and no heat downstairs even though all radiators are open fully. The house has concrete floors and the pipes run up and down the walls supplying 2 radiators per run - both radiators run independently. We have tried the following:

1.All radiators removed and flushed through with hose.

2.Cut the fill pipe near the Tee and flushed through all the flow and return pipes with mains pressure.

3.Changed pump.

4.Checked 3 way valve.

5.Checked the boiler thermostat thermostat and cut-out (boiler is cycling - hits temp of approx 82 degrees then cuts out)

6. Changed the gate valves at the pump.

7. Checked that the feed tank is clean and approximately 1 inch above the fill pipe.

8. Checked the vent pipe is clear.

9. Attempted to balance the system - by doing this we can achieve very slightly warm rads downstairs and lockshied valves almost shut upstairs creating very slightly warm upstairs.

We notice that in the manual for the Glow worm the temperature between the flow and return at the boiler should not drop below 20 degrees. This is only achievable with 2 radiators only running. If all are turned on we have a difference of approx 50 degrees -any ideas why?

The plumbing between F&E, the boiler, and pump appears to be as per the manual.

We are now beating our heads against the wall - any ideas would be gratefully received - sorry to have gone on but wanted to give as full a picture as possible.

Thanks

Julian

 

[chrishutt]

Circulation is clearly restricted by something - could the pipes be clogged with corrosion deposits? Presumably the new pump's OK (on max speed?) and all valves are open.

Is there a by-pass valve? This might be open too much. Does the circulation problem occur when only CH is on (i.e. motorised valve is only open to CH direction - no flow through HW direction)?

 

[ChrisR]

Pumping over? (Check in loft when the pump's on)

 

[Jitzer]

Hi

Thanks for the reply.

The bypass loop is shut off fully (for testing purposes). Hot water is fine - motorised valve (mid position) is working perfectly.

No corrosion in system as this has been fully flushed and checked.

 

[Jitzer]

Hi Chris

Just been up to the loft and double checked - not pumping over.

 

[chrishutt]

Does the circulation problem occur when only CH is on

You didn't reply to this point.....

 

[dal5band]

I would suspect flow restricted in the main (common) parts of the circuit if the return temp is low. Boiler-pump-valve section and common return section. You can get semi-hardened sludge "cake" that needs something up the pipe to shift it.

Try the stuff you leave in for a week to de-sludge a system - one of the Fernox range.

In the long term, I would change to 2 zone valves (C/H & H/W) - 10 rads is probably the limit for a 3way valve and they seem to give a lot of trouble - see this forum. In fact check that the valve is opening fully in the CH direction.

 

[Jitzer]

Hi Chrishutt

Sorry not too sure what you mean, however when the mid position actuator goes to the centre when heating and HW are called for the CH cools as its supplying to both CH & HW. When in HW only it heats the water with no problem. Only problem we appear to have is with CH. Hope this answers your question - sorry new to this game!

 

[chrishutt]

What happens when the 3 port valve moves to the CH only position - when the HW is off at the programmer or the cylinder stat is satisfied? Do you still have poor circulation then?

 

[Jitzer]

22mm pipework from boiler to pump is red hot, 22mm flow from the pump is red hot then it goes under the floor boards. Boiler is situated in utility room on ground floor of standard semi with pump in airing cupboard on first floor.

 

[Jitzer]

Hi Chrishutt

Yes we still have poor circulation when in the CH position and HW is off.

 

[chrishutt]

You're still not answering the question! I can't think of any other way of putting it. Any chance of an answer?

 

[Jitzer]

Hi Chrishutt

Sorry if we're not answering your question properly. I will run through the sequence - for example - 7.00am controller switched on for ch only, actuator is in position (to the right) to then supply ch only. Pipe to hw water tank is cold. When in ch mode only very poor circulation. Radiators do not get hot - mildly warm. At 9.00am heating and hw is called for, actuator moves to central position to provide for both, radiators cool even more. If programmer calls for hw only actuator moves to the far left and heating goes off.

 

[chrishutt]

Fine, that's what I wanted to know.

Do you have an isolating valve on the circuit from the motorised valve through the cylinder and back to the boiler? If so, there is one more test worth doing.

If not, you must have something obstructing the flow in the CH circuit, or the pump is not working properly. My guess is corrosion deposits in pipes. Have you actually opened CH pipework up to see if it's clear?

 

[Jitzer]

Hi chrishutt

Thankyou for your patience and time. No we do not appear to have an isolating valve. I am now wondering about an obstruction, however I did cut the feed pipe close to the tee by the pump so I could connect a hose pipe and flush each pipe individually - flow and return and there did not appear to be any blockage as the water ran freely. However I guess as it was mains pressure it could be finding a way passed the blockage.