Any experience in Central heating problems ?

badlywornroy

badlywornroy

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My CHB (using for hot water only at this time) is shutting down after 1 - 2 mins. Overheat protection it seems.

Boiler is under a Viessmann warranty. Viessmann engineer says boiler OK, suggests the pump is the problem. He cannot do more, just responsible for the boiler.

I was ready to believe the pump was the problem, it is old. New Grundfoss pump. installed, Eeek ! Boiler still shuts down.

3 way motorised valve seems fine, selector moving between heating / hot water / and central for both.

Where do I go from here ? sludged up system ? it was chemically cleaned 4 years ago. In line Magna Clense filter inspected and certainly not blocked.

Any suggestion ? and any experience of Power flushing on a (horrible) microbore system ?

Cheers
 
Is the boiler heating water in a tank or is it a combi feeding taps direct?

You may have a new pump, but xo you know that water is flowing in the circuit - can you hear it flowing for sure, or is there a chance of an airlock at or beyond the pump that it cannot overcome? I've had this happen a couple of times, where the impeller is sitting in air after it's been left all summer, and can't pump.
 
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Surely there is a thermostat on the hot water tank and this might be set too low or faulty. Do try turning it up and see if the boiler runs OK. You may still have to replace the thermostat if it is not right but it is a low cost item,

Dave
 
ancient_mariner said:
Is the boiler heating water in a tank or is it a combi feeding taps direct?

You may have a new pump, but xo you know that water is flowing in the circuit - can you hear it flowing for sure, or is there a chance of an airlock at or beyond the pump that it cannot overcome? I've had this happen a couple of times, where the impeller is sitting in air after it's been left all summer, and can't pump.
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System boiler, with stored hot water. System bleed to remove any air after new pump fitted. Pump runs ok until boiler shuts down after 1 - 2 mins.
 
Dave Canon said:
Surely there is a thermostat on the hot water tank and this might be set too low or faulty. Do try turning it up and see if the boiler runs OK. You may still have to replace the thermostat if it is not right but it is a low cost item,

Dave
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Dave, hot water tank thermostat ok, clicking in/out when turned up/down. Also activating 3 way valve.
 
Hi,

Have any isolating ball valves been knocked and restricting flow?

Is the new pump set to lowest speed setting? May need to run a little faster.

Have you tried running house heating to see if that helps clear any air trapped in the system? It'll push the air to the rads for removal.

3 way valve - was this set to manual open on refilling?

Sorry if you've done these, just throwing ideas out :)

Good luck.
 
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Few more, no offence meant for the silly questions :)

Does the pump have valves both side of it?
Were openned fully after fitting?
Is the pump fitted with flow direction the correct way?
 
What temperature has the boiler been set to? If it's high like 70c+ then if the flow isn't sufficient it will turn off. Also if the boiler is very oversized you get this issue as well as there isn't enough heat demand.

I'd turn the temperature down to about 55C and see what happens. Also check all the radiators and make sure they are turned up and the valves aren't stuck. Even the non stick valves seem to stick so they often need a small blast of WD40 and pushing down. The boiler should have a bypass valve in it so when there isn't enough demand it will send the water via the bypass and turn the burner off. With a lot of boilers it means you don't get another heating cycle for 10-15 minutes after as modern boilers have anti cycling in them. Always have one radiator fully on as it should reduce the cycling if there is somewhere for the excess heat.

Is there a diagnostic on the boiler to tell you what it thinks is wrong? Finding the installation manual for it should tell you a lot. There's usually a diagnostic flow chart so it might offer possible reasons for it misbehaving.

Finding out the minimum output on the boiler as most will reduce the burner output but some can still be kicking out 6kW of heat even on lowest level.

Also how long has the boiler been installed and how long had it worked properly before doing this?
 
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I don't think it'll be the boiler.
If water is running through the boiler it shouldn't over heat, it'll cut in and out as needed, if it's over heating and alarming out, the water isn't moving and starting to boil.
 
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When the boiler chap checked things over do you have any idea what he actually did? Full diagnostics or just a quick look over? I only ask because it seems unlikely that the boiler would reach lockout temperature so quickly so it could be a faulty lockout/temp sensor? You could, if you know where to look and know what you’re doing, temporarily loop out the overheat sensor and see if that makes any difference. Feel the flow pipe from the boiler too, is it getting hot very quickly after firing up? That would point more to a physical lack of flow or a blockage.

Slightly different scenario, but a long time back I had a Potterton Suprima boiler that would often go out in overheat. It turned out to be a design fault where the control board was mounted too close to the burner. When it warmed up, the board would flex slightly and eventually it did it enough times to crack some of the circuit tracks. When it cooled enough the board would flex back enough to re-make the circuit so it could be reset. Potterton never admitted the design fault but later introduced a Mk2 board that solved the issue. Might be worth seeing if yours is also a common issue with Viessman boilers and if there’s a fix?

Otherwise it does sound like a circulation problem. Seeing as how you’ve already replaced the pump I’d go through the various suggestions already made… check for air stuck in the pipes, partly closed valves etc. Last call would be to a proper heating engineer I guess.
 
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Gav. said:
Not sure playing inside the boiler is very wise?!
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That’s why I qualified it with “if you know what you’re doing”. ;) I used to have a gas ticket via working as a building maintenance engineer. I also designed and installed the whole gas c/h system from scratch in one of my old houses. You can do electrical work on a gas boiler yourself, but obviously you should never touch the gas side unless you’re Gas Safe registered. If in any doubt, always use a registered heating engineer though.
 
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Thank you everyone for your fulsome replies. Be assured, I have no intention of messing with kit that needs a qualified engr. I have to assume at this point that the Viessmann engineer (here on the warrranty call) knows what he is doing and the CHB is ok? I agree, time to call in a qualified engineer which I have now done.
I will update here for any future interested parties when it is fixed and/or I know the problem.
 
A bit late as you have called someone in but I would suggest turning the boiler temp down very low and, if it then runs, feeling rads & pipes to see if the warm water is getting through, especially near the pump.
Also what have you got the pump speed set to?
 
Sorry, I'm late to the party too.

I had a similar issue (albeit with different symptoms) which was an airlock. Cleared it by turning all the radiators except one off. Much gurgling, waited till all settled. Turned off boiler. Closed off the one radiator, and opened up another one. Repeat, until all radiators done. Then set back all radiators as they were, bled system, and all has been good ever since.
 
Early Update guys, I fixed it. What did I do ? . . . . err well nothing ! I turned it on this afternoon and the boiler fired up as normal, all radiators heated up as normal.

I am at a loss to understand why it didn't work and now it does, but I welcome it. I have spent £150.00 on a new Grundfoss pump unnecessarily it seems but I do not begrudge

that because the Wilo pump I took out, I inherited 12 years ago and I have no way of knowing it's actual age.

Maybe, an airlock somewhere that the new pump has dispersed ? Gawd knows. :D

Fingers crossed that the gremlins don't return. You will know because you will hear my wailing from many miles away.

Thanks again for your help and plenty of good advice given.
 
Gav. said:
PS a dying pump can cause air or fail to push water enough :)
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Yes, I agree Gav, this is why my 1st action was to change the pump yesterday. Tried it maybe 6 or so times after pump change with the boiler shutting down each time. Tried it again today and ' Bingo' Engr call cancelled, not jumping the gun I hope.
 
badlywornroy said:
Yes, I agree Gav, this is why my 1st action was to change the pump yesterday. Tried it maybe 6 or so times after pump change with the boiler shutting down each time. Tried it again today and ' Bingo' Engr call cancelled, not jumping the gun I hope.
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I hope it's sorted for you, I'd imagine gravity has stepped in and moved a few bubbles :)
 
Like you, I bought a replacement pump, though in this case it was because the pump had frozen in place over the long summer break. After buying it I had real difficulty unscrewing the connectors and gave the old unit 'one more try' at freeing off - success. From then on I always run the pump for a few seconds every couple of weeks. I've had my spare pump more than 10 years now, still sealed in the box. :D
 
ancient_mariner said:
Like you, I bought a replacement pump, though in this case it was because the pump had frozen in place over the long summer break. After buying it I had real difficulty unscrewing the connectors and gave the old unit 'one more try' at freeing off - success. From then on I always run the pump for a few seconds every couple of weeks. I've had my spare pump more than 10 years now, still sealed in the box. :D
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This is why I use my boiler for hot water ( I have an immersion heater ) System & pump standing idle all summer is far from ideal.
 
We have an immersion heater, but it only heats the top half of the tank.

This year I've kept the Rayburn in the kitchen going between 4 and 9am because the house is cold otherwise.
 
Glad it got sorted out (and free as well….result!) It does sound like it was air in the system as nothing has really changed otherwise. I’d put the three port valve in the central position and bleed the upstairs rads…. if you get any air coming out then you’ll know for certain that was the problem. Did you drain the whole system down when you changed the pump out, or just valve it off either side?
 
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