Bouncing Boiler

Morkin

Folks,

Some info. need to avoid being BSed by builder.

Current Situation:

2 storey detached. Gas boiler in kitchen. Zoned upstairs and downstairs with thermostat controlled valves.

Boiler bounces itself as frequently as every 30 seconds when operating. It shuts off then back on within 30 seconds and does so repeatedly.

The problem is most pronounced when downstairs thermo is set to ~20 and upstairs set to max (~30).

gas engineer blamed thermo controlled valves but plumber has just been in and checked all plumbing out and given it a clean bill of health.

So the questions are:

1) Is this bouncing normal behaviour? (I don't think so and have nott seen it in any other house I've been in)

2) What could be causing this behaviour?

All input appreciated,

M.